One thing that I don't think very many people consider to be an issue but I think is a bit of a big one is related to custom clients and the ability to view your own and other player's path movements.
Knowing exactly where someone is moving to is a pretty big fucking deal in this game and that little line might be a minor addition to custom clients but I feel like it has a pretty huge effect on the overall combat. Further, not everyone plays with the same clients and some clients don't have that option nor do they offer other implementations like the bow aiming line. If anyone claims they want combat to be as fair as possible then they would agree these issues need to be addressed.
Either make these implementations in the default client so they are available for all players or figure out a way to deny everyone of them. The choice is yours but please do something because the outcome of combat isn't only dictated by skill and stats when these things exist.