Power-wise, Tumble is a moderately useful but specialized skill. How often do you really want to move past or away from someone in melee anyway?.
This post summarises it for me. Whatever the characters may be able to do the opponents may be able to do also. A lot of creatures especially humanoids have character levels open to them. That weedy looking Kobold could be a twenty level characterThe way we decided if Tumble in those 3.5 days was too easy was not by what the PCs could do. It was decided to be too easy when enemies tumbled past the front line of Fighters and attacked and nearly killed the poor Wizard in a round. They thought it was too easy for bad guys to move around and attack weaker party members while ignoring the more powerful combat focused characters.
You move half your speed when tumbling (barring the penalty for full speed). Even a successful check is unlikely to get you out of a giant's reach, and it certainly won't prevent said giant from charging and easily tripping or grappling you, preventing you from trying that again and leaving you rather vulnerable. If you're that close to someone who's that dangerous, you generally need more than a Tumble check to get out of it, and as a wizard you have some options.I found that when my wizard ended up toe-to-toe with a giant who will absolutely certainly kill me in one round with a full sequence attack, moving away seemed to be a good plan. In general, it's nice to tumble because you then only take one hit, as opposed to three. I pretty much always take Tumble with a wizard, even cross-class. At reasonably high level you can auto-combat-cast in their face then auto-tumble away. I recommend it.
I have always found the DC15 too low. In my opinion, the DCS in D&D 2.5 are a bit too low, like the designers never really expected characters to hit the higher levels.
True. Why should a high level character ever fail at things that he could sometimes succeed in at lower levels?I doubt that's the case. Rather, I think they wanted relatively routine uses of skills to decline in importance for powerful, skilled adventurers. All you have to do is look at page 31 of the DMG to see that they did think of tasks with their DCs and when characters should be able to accomplish them without much fuss.
You move half your speed when tumbling (barring the penalty for full speed). Even a successful check is unlikely to get you out of a giant's reach, and it certainly won't prevent said giant from charging and easily tripping or grappling you,