Right swing needs to be sped up a tad before I would advocate toning down the left swing. Even so, it's similar to how 2h and poles have one of the side swings that is faster than the other. I assume people want melee to be fast, not slow everything down.
The best case would be giving 1h completely different animations without the shield, but that requires more work. Easier sweetspots and less weapon stun are the easiest quick fixes I can imagine. 1h is fine enough in duels and suffers against multiple opponents due to the stun.