What does this mean ? let me explain to you : Balance is an overall stat and efficiency state.
2H Weapons are way more effective than 2 x 1H stuff. I don't say that you are incorrect with the numerical loss, I say, there is no point granting a more powerful item more power, it would unbalance it.
I could agree with you, only if you made correct statement : 2H Psyker stuff is a little bit unbalanced as it lacks efficiency comparing to other classes. If you wanted to point out that the Psyker stuff is at stake here, you had to say it clearly.
You stated that ALL the 2H stuff needed a major affix or a double affix.
On this we can't agree with you.

A game is like a chemical, it needs balance to works fine, if you unbalance things, well it never ends well...
You can't speak only of numerical thing, cause balance is, like I said, an overall thing. It's not purely numbers. You have to take in account of all the skills, passives, bonus etc... that come with it. You have to take in account, the feelings of the final chemical, does it works good ? is it working TOO good ? or is it working pretty bad ?
ATM, 2H weaps for Assassin and Crusaders are way more effective than 2 x 1H. You can't disagree on that.

If your problem is correlated to the 2h Psyker's stuff, that is another problem, and maybe, this stuff needs a buff.
I can't tell actually, I've just maxed out my Assassin, got all the stuff and maxed it, and I'm now working on the crusader.
Psyker will be my next and last class to max out. So I can say for the two first classes mentioned above, that their 2H stuff doesn't need any buff.

That's why I can only disagree with your first assessment of the problem. But I can go with you if you say that the Psyker is the problem. I've tried him a little bit but am playing with 2 x 1h cause I prefer this style, didn't even try the staff. So I can't compare, and if you're a hard Psyker player, I can only rely to you and to your experience.

2h weaps are OP. They don't need "major" or double affixes.

I deal far more dmg and clean a lot faster with my sniper than having 2 pistols or having 2 sword or a mix.
Sorry I have to disagree with you on this statement.

1) Dual Melee, Sword and Board - it's really hard to find a dominate build, just based on 2 weird affixes. They differ dramatically, and are balanced just by 'feeling', since they mostly don't have measurable or calculable way - whole balancing must be done experimental, that takes huge amount of time, even when there are *some* numericals that could give initial comparatives...

While making a feasible (dominant, even) build using 2 weapons, it requires a good idea, lot of thinking and tweaking and... Players which do that alone (and not copy it from much-hated youtube) *deserve* that (very strong build).

Since we saw NeoCore data on weapon and gear (and in the later time perhaps refined ones, eg. how much affix this-and-that existing on players equipment, and what isn't present at all; same with skilltrees etc.) they can easily decide (or publish) usage of 2-handers vs dual 1-handers. Snakefist believes that 2-handers are 2x or more represented than dualing ones - which means they do quite alright and don't need any boost. It's an estimate, and NeoCore can easily put real data behind this, or prove it wrong.

2) Dual Rods/Wands - they are used much and offer much and this is probably caused by greatly overpowered skill, namely Wychfire, and mostly weak basic skill. In this case, 2-handers indeed need a buff, perhaps not 2nd affix - but it may be a solution.

3) Dual Pistols - Mighy Snakefist will skip this, due to limited experience.

4) Dual-wielding two different 1-handed Swords, for instance, does give 2 (strange) affixes, but cripple player with 2*(skill1 + skill2) - not interesting at all, since all 1st skill for sword are single attack and all 2nd some kind of slash. In this case, He'd like to have one weapon in 'off' hand, doing 1st and 2nd skill, and other in 'main' hand, giving 3rd and 4th skill. This would make 'custom' dual swords build, effectively increasing number of possible ones greatly.

Sword + Board offers a little, since there are just 3 1H-melee weapons and 2 shields. For gun/sword or gun/shield situation would be much better with 'main' and 'off' hands, like above.

5) No improving is needed for 2H-weapon, as long as it isn't PROVEN they're actually in disadvantage compared with 2*1H - which NeoCore can easily prove or disapprove, as they once did. Basic experience in coop tells me that rarely people use 2x1H, they tend to have at least 1x2H. \

Except for staves/rods, which inherent skills should be looked at, and fixed.

This WAS a problem in Elder Scrolls online you got bonuses based off the number of set items you equiped. 2h weapons took up 2 slots but only gave 1 bonus set perk....so sword/board got 2 perk slots in total. +1 on 2h weapons.

I would like to see MAJOR and MINOR weapon Affixs added to 2h weapons melee, ranged, and staves. 

Definitely yes, 2h and 1h should be more balanced, and giving 2h double affix stats or 2 affixes would be a start.

The concept is fine as it is, just needs balancing in some cases.