RnF,
I'm looking for some elucidation. So, let me give my opinion on the matter and if I'm missing any important information, lemme know.
Is dual-wielding that superior to greatweapons in Vanilla TL2? I've not gotten to high levels so I don't know about later-level play, but I always found a single, very fast main-hand or a big slow two-hander to be my preferred weapon setups. I always kinda thought dual-wielding sucked (y'know, up to level 20).
Someone reverse engineered the damage calcs and showed that dual-wielding gets kicked in the nuts when it comes to calculating DPS, too. It averages the DPS between the two weapons. While this doesn't matter so much if you have TWO good weapons, it does require you to have TWO good weapons just to equal the DPS of ONE good weapon. Why bother dual-wielding if you don't get added DPS? Sword and board gives you the same DPS and then Block to top it off (which is huge).
I bring this up because the real beast in vanilla seems to be sword and board because the superior DPS scaling one-handers get from flat damage gems and affixes combined with the huge defensive benefits you get from block.
Now, we're redoing the stats and removing both dodge AND block bonuses from primary player stats. So, sword and board is going to take a huge hit in power. The block chance is going to be capped by item bonuses, spells and skills.
We can now control the difference in power between these three loadout options. Especially if we remove flat damage affixes and replace them with percent damage affixes across the board. The flat damage affixes and embers caused power creep that favored one handers because their faster weapon speed. Erase those and they're not an issue.
So, as it is now, with the overhaul you're doing (and assuming you remove flat damage bonuses), we have this situation:
--Sword and board gets 2 items worth of affixes and 100% dps. AND some defense from a shield.
--Dual wielding gets 2 items worth of affixes and 100% dps. And a little extra DPS from execute which is now a stat they have to gear for.
--Greatweapons get 1 item worth of affixes and ~150% dps (or however high you set it). And, like wolven said, greater arc, secondary damage and range. And higher base damage, but that'll be unimportant if you change out flat armor for percent damage reduction.
On paper, I think having double the weapon affixes when dual-wielding helps to make it pretty much equal to using a greatweapon that only gets 1 item worth of affixes. Also, dual-wielding doesn't have 100% more affixes than two-handers. I think we have to count all the affixes a character can have on their armor as well.
You have 12 item slots total, but the armor and jewelry slots don't get as many or as good of affixes as the weapons, so let's count them for 1/2 (this is a total guess, if you know the actual ratio, I'd love to know it). So you have 7 'weapons' worth of affixes if you use two one-handers or sword and board, or you have 6 'weapons' worth of affixes. If this is all correct, then it's more like a character using two-handers has 15% less affix value than one who's dual-wielding.
What I suggest is proceeding with caution for the moment. With all the other changes you're making to items and stats, the problems with greatweapons may have already been sorted out.
If you find that they have not been sorted out, then I would suggest either adding just a couple affixes or increasing the 2-handers' base weapon damage to make up the difference.