It doesn't matter if it's all of them. You asked which group benefits more. That means you're *suppose* to cherry-pick the best. On both sides. If you're deliberately avoiding the good stuff... well, of COURSE you'll limit the power. That'd be another house rule.
Ok... so you got a powerful enough TWFer. Does it do anything else cool? At all? Because at level 20, hitting things with swords has long since stopped being all that interesting, useful, or effective. I'll grant you, it keeps the ranger combat effective. But it isn't as good a boost, linearly, as... let's see... sandstorm has Walker in the Waste (at level 10 you become a superior breed of liche- complete with phylactery). Worth two caster levels. Beastly if you keep the CL.
SandShaper (another sandstorm) costs 3 levels. But adds a huge list of new spells. STRONG new spells at that. Easily takes your sorcerer into the T1 range and possibly beyond if you don't pay that caster level cost.
Scion of Tem-Et-Nu (more sandstorm)- 1/2 casting. Full BAB. Fast Healing. Total Gish wet dream. The lost CLs are what makes it not worth it. Suddenly, godlike.
Your TWFer is still, at best, a T3 character. Still gonna get its ass kicked by a sorc. Given how weak TWF is, even perfectly optimized, and the price tags associated with double weapons... I bet you it's still not as good as an optimized barbarian with a two hander. So you didn't even increase its tier a full step.
... How do you count a CLERIC that multiclasses to a cleric oriented PrC to suddenly be counted as a paladin? It's still a cleric. Just an even more ungodly one. Cleric casting, cleric features, cleric starting class. If you find a way to have a character start as an ordinary paladin and gain T1 casting... THEN you have an argument. But this just takes a cleric and gives it Full BAB, better HD, and some great class features.
... It doesn't matter the "group's preferred power level"- that's a house rule. You have to leave all (legal) rules in the game in order to legitimately compare effective changes to power levels with your house rule.
At best you can argue a "comparatively speaking" point. A thousand dollars means a lot more to someone on the poverty line than half a million dollars means to Donald Trump. That's what your rule does, metaphorically.