For me balance means letting the player's progress match the amount of effort put into the game.
This of course is subjective ... and I do find that currently there is a nice grind required for most things. But even so I find that I can progress a little too quickly to higher level stuff ("stuff" is the correct technical term)
So with that in mind my only real criticism is around "repairs".
Finding a gun early on opens a lot of doors. Too many perhaps. So my suggestion is that a player should only be able to repair that which they are able to craft, and the repair should require something more specific. Guns should require gun parts to repair, military armor should require military fibre, and so on.
The challenge for TFP is of course finding the point where the grind becomes boring... Nobody wants to play a game where weeks and weeks of grinding becomes too repetitive. I personally think it is not bad as it stands. People stay engrossed with the game and become long term players. New players progress fast enough to not give up right away.
So how much imbalance is there? Not too much, but as I said on default difficulty the progress is perhaps slightly too fast.
FWIW - I don't play PVP and would never play a game where new players with no skill and low level are directly pitted against advanced high level players. So I firstly don't think 7dtd is PvP friendly and secondly my above post relates specificly to survival / solo / co-operative play, not PvP.