In MM3 if you held down S key you could get 2 shots for the price of 1, which is why I avoided using it. Is something similar going on in MM6? I'd hold down the A key to speed up fight, but I noticed they kind of made the enemies fall faster. Or am I just imagining things?

Of course, when holding the key down in real-time you will always attack as soon as you possibly can, other than that I would believe you are imagining things. BUT, I know there's a bug in Might and Magic 6 with recovery times, I experienced it quite a bit with Blasters. Blasters in particular have a very short recovery time (30). Normally weapons can't go below 30, but Blasters and Bows can, I believe. So with a sufficient amount of Speed and the Haste spell, it's possible to keep shooting a stream of shots extremely rapidly, when holding the A key in real-time. Don't know if it has been fixed in the patch.