We had some problems and we didn't have time for most of the stuff you point out.
Knowing which fighter is yours can be pretty confusing (we didn't even change the gloves color...).
There is an slowdown mechanic (when your fists collide with your enemy fists) but we didn't do any different visual feedback for this so it's not easy to understand,
There is also a simple health and recovering system underneath that is totally invisible for players.
But well, that is what happens in game jams! And it is a part of the jam developing charm, so I am glad you liked it anyways :D