GokuTheKilleri think a lot of bans were arbitrary beyond a handful of truly problematic weapons, and the main reason some weapons were banned in the past, was that it would either conflict with bad players' theories like gru or buffalo steak needing to be banned cuz of heavy to mid, or they'd be thought of as unfun and people thought that answer was satisfactory.
This is a good point, however majority of weapons have actually been explored reasonably well now, even if it took us two decades. The most restrictive league etf2l bans just 30 unlocks out of 151, I think all but 9 of these have been allowed at some point. Yes the remaining weapons have not been fully explored, but the majority have such problematic stats that their effect on the game is extremely unlikely to be positive. Here's a quick list of weapons that have never been unbanned in a major 6s league to my knowledge.
reserve shooter
soda popper
crit a cola
cleaver
milk
whip
fists of steel
short circuit
wrangler