Yeah, Cassie and Marco were definitely supposed to be similar to Katherine and Michael with their respective worldviews, they've stated as much in interviews. Even the names are vaguely similar. Kinda makes it funny that they never got along in-universe. XD
Look at the Animorphs' development through the series.
- Jake steps up as leader, and while he was kinda flat and boring early, he turned from an idealistic jock into a hardened veteran, crippled by desperation and self-doubt, and ends up unable to function without a war going on.
- Ax is a proud young cadet just trying to do his duty and make his species proud even as he was stranded on an alien planet, burdened by feelings of inadequacy that he tries to overcompensate for, and ends up being forced to choose between the friends he made or the species he was brought up to serve.
- Rachel finds out she's really good at killing stuff and is disgusted by herself for liking the thrill of it, but keeps that side of herself hidden so that she doesn't drag the team's morale down with her, and ends up drowning in a pit of self-sacrifice all by herself.
- Tobias has to learn to deal with the hawk body and adjust to his new life, hoping desperately that he can be strong enough to help his friends and not be a burden, and barely maintains his sanity through all the crap that he goes through.
- Marco has to try to keep his deeply personal stake in the war from getting his friends killed, and keep his anger, selfishness and denial from clouding his objectivity, all while trying to see if he can still keep a positive attitude about life to keep everyone else from sinking into depression.
They all have their own journey through the war that totally changes them. By the end of the series, they are all completely different people.
All except for Cassie. She starts off idealistic, naive, and and constantly trying to force others to live by her arbitrary double-standards, utterly rejecting everyone elses' views as invalid, and never stops. She does that straight through to the end of the series, and never learns from her mistakes, because they have a habit of magically working out for the best, and that's just attributed to her being highly perceptive when there's really no way she could have predicted anything (see my examples above). Her special attributes just pile up to compensate for her lack of any character-based struggle (
estreen, animal whisperer, infallibly intuitive, sub-temporally grounded, etc.). She could have had her own story arc, maybe something with the Yeerk Peace Movement, but that never went anywhere. Books #19 and #29 were good. Unfortunately, it felt like Applegate ran out of ideas for that, and every other Cassie book apart from #50 was pure filler. It's almost like she didn't know what to do with her own self-insert character.
It's kinda similar to the difference between Batman and Superman. The writers have Batman deal with a whole gallery of villains that all reflect some part of his personality that he's trying to overcome or come to terms with, and try not to go insane from stress. He always thinks his way through things and makes difficult decisions that even got him kicked off the Justice League. With Superman, their solution for decades has always been to just make him punch something harder than he's ever punched before, or get some new BS power on top of his already ridiculous collection. Flying and super-strength/invincibility? Totally, that's iconic for him. Super speed? Sure, gotta fly fast. Laser eyes? Well, he is solar-powered, so it's thematic, I guess. X-ray vision? Um... Frost breath? Lie detection/telepathy? Seeing peoples'
souls? Getting stronger to the point where he can punch planets into dust and literally bench press more weight than probably even exists in estimates of the known universe? Yeah. That's all new powers as the plot demands, and he's a total mess nowadays. He literally just has to be stronger than whoever he's facing.
[spoiler]And provided his one token weakness kryptonite isn't there, he always is. Although there was that one time some minor nobody villain managed to beat him to death in a fistfight, but that didn't last long for whatever reason. Apparently, that whole arc was a mess anyway and I think it got retconned.[/spoiler]
Batman doesn't get stronger as his story goes on (origin story aside, obviously). If anything, he gets weaker as he ages. His knees actually get totally shot from all the injuring, face-kicking and rooftop-parkouring he does, leaving him crippled with arthritis if he doesn't have his knee braces. He has to work to figure out ways around all his weaknesses as a human being and a character, rather than just getting stronger to meet the challenge.
And that's a problem Cassie faces. Most of the stories where she shines are specifically set up for her to take advantage of some special attribute she had dumped on her. In #4, she can hear Ax for unexplained reasons, when it really only kinda makes sense that Tobias would, and then the whole whale thing happens. In #7, she figured out the Ellimist's game, even though Marco (the paranoid analytical one) really should have been the first one to see that there was another level there. Not even gonna go near #9. Book #19, her "intuitive" leap of faith gets Aftran to trust her, and luck makes everything work out. Book #29 was awesome because the ghostwriter knew what they were doing, but the plot still centered around setting things up for her area of expertise. Book #34, she saves the day because she's an
estreen. In MegaMorphs #4, she unwittingly saves the day by doing nothing all book long, just by being sub-temporally grounded. There's more, but this comment is long enough as-is.
So yeah. I guess the obvious conclusion we can draw from this is, Cassie is actually Superman. NEW HEADCANON XD [/sarcasm]
Bond and Bourne are both definitely Sues, albeit slightly different kinds. Not gonna argue that point. Bourne is less so in his movies (he at least acts like a real person in the movies, the books are kinda weird and convoluted), so I like him as an action hero and enjoy that power fantasy (in fact, I even started an original story based on the character concept), but yeah. I haven't really watched the Bond movies, so I can't say much there, but the character never interested me from what I saw. Too much of a slick alcoholic womanizer, the kind of scumbag the writer wished they could get away with being, as opposed to being a strong character who also happens to be a scumbag. My sister read one of the books by Ian Fleming, and told me that's basically the case, along with some really silly amateurish prose. XD
You said that the difference between a good character and a Sue is a matter of time, skilled writers, and people agreeing with the fantasy. But time adds nothing. You can have an excellent character-based story that's only a couple pages long. Check out Ray Bradbury for some excellent short fiction. What do skilled writers add, if it's just a matter of people agreeing with them? Good writing is much more than just appealing to the lowest common denominator. It will make you millions of sales a la Twilight/Fifty Shades/Superman/Bond, but it won't make your character not a Sue. Good writing and appealing to the lowest common denominator aren't mutually exclusive concepts, but they accomplish different things, and don't really substitute each other well.
Writing is a fun, cathartic experience. Trust me, I know that well. But it is
so much more than just that. It's art. Anyone can whip out a stick figure and call it good, and you can produce some really
good stuff with stick figures. But trying to represent a person or object with accuracy takes objective technique. A power fantasy that doesn't care enough to explore anything further is how you get a Sue, the literary equivalent of a stick figure the artist never cared enough to improve. My first attempts at writing were awful for just that reason. I had no themes, no real plot beyond kids turning into dragons and killing people, and no character development of any kind. I identified with the power fantasy completely (still do, in fact) but the story was boring, predictable, and had no point in existing. All of it was just schlock no one would bother to read if they didn't already know me. Fantasy alone doesn't give the substance a good story or character needs. Any story starts with the author sitting down and figuring out what they find
cool. Then, they build on that.
Coolness is a foundation and a means, not necessarily the end. Yes, the reader's enjoyment is subjective and based on how much they agree with the author's idea of
cool, but there is an objective basis for how much the author decides to expand on things, and that increases audience interest significantly.
TL;DR: The other animorphs all have more to them than just being self-inserts with superpowers. Every one of them has a story arc and can stand on their own. Cassie wasn't given that chance, just loaded down with people saying she's special, when she actually had much more potential as a character. It might even be the case that Applegate didn't even care that much about her as a character. It's sad, and I want to fix that.
Okay, how the heck did this comment become over 3 pages long? Sorry 'bout that. My comments have a tendency to explode.