I really like this game for the most part, but one thing that always ruins it for me is the buggy, unresponsive combat, control and pathfinding of legions.

Did anyone ever attempt to make an unofficial patch to fix this ? It's driving me nuts.

Sure, there were attempts to make patches, but those have been lost to the sands of the internet.

Your better bet would be to give either Julius (Open Source faithful port) or Augustus (Introduces save-seperating features) in hopes of seeing which one of those two projects may fix your issues.