Plane Sailing said:
I think it is about more than this though. If it were just the tumble past someone, I'd agree - the problem (for me) comes from the standard PHB rendering that means that any attempt to tumble through a solid line of enemies *always gets past them*. Worst case is you get some AoO against you which could well miss (if you have mobility and are "fighting full defense" (assuming allowed by your DM) you get +10 to your AC against those AoO anyway.
So I think it is the "tumble through" which is too powerful. Roll a 1 and still get through everyone.
Why is this a big deal either? If the enemy would rather smack you than grapple or trip you as their AoO, then that's their decision. DC 25 is pretty high already. My 12th level rogue only has about +15 or 16 to tumble. So, that's about a 50% shot. And, he doesn't have Mobility or Spring Attack. Except in the case of mid-high level rogues/bards/monks who choose to spend a lot of points in tumble (while losing out on other useful skills), it isn't that hard to stop many tumblers from coming through your square, IF you really want to.