Moermannatasha, jarate, sydney sleeper, cow mangler, scorch shot, bonk, milk, crit a cola, pretty boy pistol, detonator, soda popper, market gardner, whip, reserve shooter
Most of those are bad examples:
Jarate, Milk, Cola and Soda Popper all give clearly OP utility.
Whip completely changes the game with slow classes being sped up and way more bombing options available, debate can be had whether it would be positive or negative but would be huge regardless.
Bonk was always banned because it allowed player to get behind on the flank for free, and Reserve Shooter could deny bombers with mini crits. Both have been nerfed to an extent that they might not even be very strong atm, but I don't think their fundamental mechanics are popular.
Market Gardener, Cow Mangler and PBPP are all borderline. ETF2L has played with them extensively and eventually leaned towards ban because they are marginally OP.
So I think that leaves 4 that are perhaps 'banned because annoying'
Natascha, Sydney Sleeper, Scorch Shot and Detonator
There might be other justifications I'm not aware of, but they are all extremely annoying to play against.
Also, if an admin or anyone does have an archive of why all the weapons are banned it would be nice to have on a public whitelist