I have never seen a problem with tumble really. It can be pretty easy against a single opponent if you have enough movement but once you need to get through multiple threat ranges at once, or need to move farther, or have to actually go through someone it takes a very high level character with a lot of investment to be able to do it a reasonable amount of the time.
I do not mind a character with a lot of ranks in tumble being able to move around another character with relative ease after a certain point much like I do not mind a character with a lot of ranks in concentration being able to cast defensively with ease after a certain point either.
At some point you just become very good at avoiding opening yourself to attacks.
It looks like there are a few different people adding base attack bonus directly to the calculation. Since every level your maximum rank goes up by 1 for tumble while base attack bonus can also go up by 1 each level it would seem that such a change would make tumble only useful against opponents who are much lower level. To me that is a bad change especially since tumble has a cost while gaining base attack bonus happens basically for free.