Adapt and win.
Whine and lose.
1hander are still very effective against 2h, but you have to train and learn how.
Footwork, timing, game mechanics.
Footwork is essential, turn around your foe, sidestep, foward fast, backward when needed...
Timing, strike at the right moment, right after a block, or after your foe miss you, but you got to be fast reactive and concentrate.
Game mechanics, sometimes 2h can strike twice cos you're stun (or stone, that's another problem). When you land a hit, you can strike again, your foe doesn't have the time to strike when he's wounded (call it the double tap...)
Btw, my main is a 1hander but when i play my 2hander, shielders are what i hate the most...i hate that sidesword spammer!