I strongly agree that more could have and should have been done with Aftran, the Yeerk Peace Movement and the Auxiliaries.
And I agree the oatmeal thing shouldn't have just been throw naway when they were finished with it.
I also feel like it would have been nice to see the Andalites do something about earth beyond mourn Elfangor. If that group of undesireables can make the trip to and from earth why not at least a real commando squad? Why don't the Andalites that do show up or are already stranded on earth do more/anything respectively to stop the Yeerks? Other than Ax obviously, the Andalites act like the war on earth doesnt matter, but what other class 5 species do we hear of the Yeerks trying to take (besides the Anati if indeed they were even a species) the Andalites don't even consider going there to avenge the
Galaxy Tree, they just seem to say "Oh, well there's a cadet and some human youths, it's probably fine."
This bothered me, those two Andalites who's names I refuse to waste the brain cells remembering (out of contempt) were content to live on earth and let the Yeerks take over, even sell out the Animorphs, those other four show up and do what? Snipe a couple hork-bajir and crash a ship? The Andalites main excuse for not defending earth at all (never mind properly, I'm going for "at all" once
Galaxy Tree went down it's like they said "screw it, we lost Elfangor, that place is too rough") was that the trip would take a long time, that went out the window Ax's girlfriend showed up in 38 (I think?), granted that was more than halfway through the series, do you really mean to tell me that when they can muster thirty dome ships around the homeworld in addition to the homeworld garrison which Ax mentions at one point as being large, and in addition to the garrison occupying the Yeerk world, they can't send a single infiltrator with a commando squad, and the mere idea of sending a portion of that to Earth instead of all of it to Anati is totally beyond them?
Some allies.