Now this is a smaller problem in the PVE as well but even worse in versus, if the host quits the game then no one gets xp, this has happened to me recently 3 times in a row preventing me from leveling.
I suggest a simple fix of giving some xp after each round as well as a lump at the end, right now you get 200xp for each round after the match ends, instead it could be 100 at the end of each round and a further 100 at the end of the game for example. That way at least anyone who has played for a couple of rounds just to be disconnected for one reason or another isn’t getting nothing.