Yeah, and let's not forget that Rachel is also related to Tom. She has connections, albeit not as strong, to the stacked deck as well.
Rachel was a huge part of the team, Her morphs were the power morphs, were she not in the story, they probably wouldn't have survived many of the missions.
In regards to the MM4 Cassie grounding: I thought that was just a cool twist. It may have been unnecessary, and yeah, if Jake had succeded, the same result would've come about, but I thought that last twist was a very cool addition. And it also shows a "Mind over Matter" type of thing. Even though Cassie was grounded, if she didn't have the prescence of mind, and the will power, she would've just accepted death, and the war would've ended there. But she overpowered the vision, and took control. I thought it was a very cool addition.
Although, I also am a fan of Cassie, so I can understand that if you largely disliked Cassie, and were glad she died, how that ending would put you off.