Why couldn't Jake have gone? (Either with or without Rachel?) It just would have seemed far more appropriate, consistent, and heroic. Then again perhaps it wasn't supposed to be (though considering the rest of the series I don't buy it).
And I still think Marco could've gone too. He would've gone even if he realized it was a suicide mission (or close enough).
Granted: it couldn't have possibly been Cassie, Ax or Tobias (because of the Taxxon thing - then again Ax could have done that part too)
You're absolutely right about Jake. And before anyone tries to argue that Jake was needed to run the mission on the Yeerk Pool ship, think again. Did the Animorphs really need Jake to be there? NO. Think hard. Think about the mission every step of the way and you'll realize that no, they really could have done without him if it came down to it. He wasn't entirely essential to the plot there.
1) They'd already been through dozens of missions without Jake, and they made it out alive just fine. Besides, Cassie was "the closet thing to having [Jake] there." His own words. She could make the right decisions, as well as Marco. Together they equaled Jake. And if you ask me, neither Marco or Cassie would've flushed a thousand Yeerks into cold space. That would've saved Jake from falling into despair after the war was over, if he hadn't been there.
2) There were no other major decisions to be made. Everything could have been planned out beforehand, as it already was. Hell, Marco could've morphed Jake to fool Tom.
Jake could've accompanied Rachel to kill Tom. Or at least replaced her. So either he was just a huge coward (didn't even have a plan to help her escape? What kind of cousin is that?) or KA missed out on some serious brainstorming. Like I said, none of the characters were being themselves, except Rachel in her death scene. She was so calm, smart, SANE. The only part about Jake I liked in the end was that speech he gave right before the battle started. He was so adamant on winning and it made him look crazy as f***, but I respected his will. He just wanted to win, no matter the cost. Put all the b.s. aside to do what you have to do. Strangely admirable.