What if instead of calling for help and waiting to be rescued, Ax used his shark morph and left on his own? How do you think he'd fair without any guidance from the animorphs? What if he was less willing to join the group, and spent books 4-8 trying to defeat the Yeerks on his own? Possibly trying to take down the pool by himself, or something. We know that much of the ceiling of the pool was held up by forcefields early in the series. I once came up with the idea of finding a generator within the complex, and destroying it to shut down the forcefields holding the place up.
In MM4, he found his way to a parked bladeship on the mall. I forget why the bladeship was parked there, but the way it played out for him in MM4 likely wouldn't happen in a timeline where the animorphs actively resisted the Yeerks.
If you were going to do it differently, how would you do it?