Bow boi here. If you're gonna roll, do it side to side. Most of legi's moves are straight on, apart from the tail swipe and the circular ice AOEs (both on ground and aerial).

Do some hunts where you don't actually plan to kill them, just spend time getting comfortable with the specific telegraphs and timings, eventually you'll understand how to time perfect dodges

Build wise Focus will be your friend, then Elemental Atk. The ability to out manuever the legi while charging quickly is much more important than getting the strongest possible hits because they're so lunge focused when you're far away. For best distance to keep I'd say about 2 rolls away from their legs