Since the most recent weight-based(I think?) turnspeed change, overheads are, in my opinion, stronger than the all-mighty left-swing. They also frequently hit the bad guy's brainbox, are more difficult to block, and are easily combined with holds and feints.
Of course, in a group-fight, left-swing spam is often the most viable option, especially when outnumbered. Of course you're going to perform the most reliable and quickest attack in that situation.
Polearms have the right-swing in an even more powerful position than 1h's left-swing, I think. This does not mean it needs to be changed. Every class of melee weapon will have an animation that the user deems most powerful, or at least that they favor the most.