There's 1 1-slot 2hander + 3 1handers with a 2h secondary mode.
All 1hs are 1-slot or less.
There's 4 polearms that are 1 slot.
Now ask yourself this. Among the archers and crossbowmen that take PS and some melee wpf; which is the most common? One would guess 1handers since there's so many options there: swords, maces, hammers, picks, axes etc. Yet 90% of these archers/xbowers take 2h. Let's just assume it's not because 2h is more powerful than the other melee classes just by being 2handers. That means that 2h must have the strongest/most varied/most efficient 1-slot items. Why would we then give them more, instead of giving better alternatives in 1h or poles?