Does anybody have a problem with the Tumble skill? It doesn't seem to fit the D&D tolkien-esque universe at all. You've got a Daryl-Hannah-Type-In-Blade-Runner come flopping your way, doing the cheerleader thing, and you can't touch her with an Attack of Opportunity as you moves through your square?
I have some problems with the Tumble skill as written, but not the ones you outline.
First, D&D can be used to fit the sort of Tolkien-lite universe of concensus fantasy, but it also can be broadly adapted to just about any fantasy paradygm with at least the accuracy that it models Tolkien (and in many cases more accuracy).
Secondly, Tumble is the skill of evading attacks through acts of agility. This in no fashion has to represent doing flips and somersaults. How you describe the act of using tumble to evade an attack is up to you at the DM. You don't have to describe it as doing somersalts, and you probably won't if you have gritty combat as part of your settings fluff. Instead you'll describe it as bobbing, weaving, and feinting to make yourself an impossible target.
If her skill is high enough, she can overcome the armor penalty and tumble right by you in armor, albeit light armor.
Sure, but if she's more than 6th level or so, she probably isn't from either the real world or the Tolkien universe. Above 6th level, you are dealing with 'The Batman' and other superheroic characters.
And what about her equipment? Are her daggers tied to their scabbards? Do her belt pouches jingle, make a lot of noise, and flap back and forth beating her in the gut and groin?
Presumably the skill of tumble includes training in how to stow your gear in such a way that it doesn't interfere with your tumbling.
It seems to me that the DM should be very strict on this skill and its use, limiting what the chartacter carries (even more than the weight limitations--an almost empty backback would seem to screw one up).
What do you think?
I think you are reverse engineering what you think Tumble represent - Darryl Hannah style flips and such during combat - and coming to the conclusion that its 'not realistic' (in your setting). Rather than doing that, I think you should accept that your fluff is not realistic and adopt more realistic fluff for the mechanics. Start with the assumption of what it mechanically allows you to do and then work out what fluff that represents in your setting.
My biggest problem with tumble is that the difficulty doesn't scale. Rather than an opposed roll, I keep a single roll with a difficulty that scales with the target's BAB.