re
Pax,
I don't disagree that the whole Tumbling mechanic is unrealistic, but if you wan't realism don't even allow Tumbling. Real people do not Tumble while fighting. In fact, real people would die if they tumbled around during a sword fight, especially with demons.
Tumbling is cinematic. Period. Even the Asian martial skills did not teach tumbling as a common means of fighting your opponent. The Samurai and Shao Lin did not tumble around their enemies like you see in the movies. Tumbling is very bad in a real fight. There is no way to add realism to tumbling, if you want realism you don't include it.
Adding an opposed tumble check will add nothing to your game but another dice mechanic. You don't need it.
You and I seem to play in very different games. My monk/rogue/ninja spy can barely enter combat any more without getting smashed on. The main fighters with their big bad ass 2-handed energy weapons, heavy armor, and strength enhancing items are way overshadowing my character. My guy is primarily their for scouting and trap removal. If I get a chance to shine in combat, it is rare.
I don't know how you're rogue is even able to land all that many hits on the bad guys at your level. They certainly must not be prepared and your magic items must be vastly superior to theirs. I'm getting my ass handed to me. I don't know if my DM is particularly mean, but I know I can't even begin to compete with the fighters, clerics and wizards of our group. They get to have all the combat fun while I mostly make sure that our travel path is safe and open all chests.
I have found that at high level, Tumble is about as useful as Spot.
Me "I spotted the creature."
DM "It attacks you. It gets two tentacle hits and a bite. It hit with both tentacles for 32 pts and it bit you for 21 more, make your grapple check. You've been swalloed whole."
Me "At least I saw it."
That's about how useful tumbling is for me right now. If you're rogue tumbles into sneak attack position with an elder prismatic dragon, just have the dragon a round of attacks his way. He won't do it again, no matter how easy it is to do.
Tumbling is easy, but relatively useless at high level. The monsters are just too friggin tough.