DreadArchon said:
The DC to Tumble Through at half speed is 25. You're comparing it to Overrun, which lets you move twice that fast. The DC to Tumble Through at the same rate as an Overrun is 35. The Epic tables start at DC 30. Therefore, to Tumble as a substitute for Overrun requires an Epic check. This assumes, of course, that conditions are ideal, which they often are not.
You are focusing on the wrong point. Yes, the abilities are slightly different.
But from a combat perspective, Overrun has a defense, preventing a Rogue from moving to the opposite side of a defender by moving through him. Tumble Through does not have this defense. Additionally, there are not too many ways to avoid the AoO with Overrun, but it is possibly to avoid the AoO of Tumble Through (again, making it more potent than Overrun).
Game balance is about pros and cons. Offenses and defenses. When an ability is added to the game that is difficult to prevent or defend against, it should be reviewed for balance.
DreadArchon said:
And level 10? You'll need either feats or max (Elf) dex to get it by that point (both if you lack magic items to boost it), and you're still moving at only half speed, which makes it slower than an Overrun. Plus, then you find that you've put a great deal of effort into something which isn't even all that useful.
Utility is not the point. Game mechanics should not necessarily depend on how often one uses them. Just because one PC might use it a few times per year, another PC might often use it a few times per combat.
Plus, you mentioned Tumble Through being half movement twice here . It is only required to be half movement through the square of the opponent. This is closer to -5 movement than half for situations where getting through the opponent is the goal as opposed to avoiding AoOs. For example, 30 Move tends to go down to 25, not 15 (and by the time Rogues use Tumble Through a lot, they might have boosts to their movement, 40 going to 35 or even 60 going to 55).
Sometimes, a Rogue will also Tumble through the square in front of the target as well in order to avoid an AoO approaching the target, but that still only drops it from 30 to 20 for medium sized characters.