Flying Guillotine:
Does 50 base + 40 bleed (long range does 68+54) and recharges in 6s. Way too easy to just spam down long corridors or through chokes to basically win fights against enemies with no medic around. Essentially it would turn flank fights to having your scouts throw their cleaver until they hit something and then walking in. There is no reason to allow a weapon that is basically luck based dominate the flank.
As for the alternatives, the pistol is terrible and even with the best aim you still aren't going to get over 30% of your shots hit, i.e. you usually aren't going to do more than 50dmg at a time. The winger is even worse damage wise, yet most scouts use it for the jump height which really is only useful when out of a fight to save time. If there is a scout secondary that should be allowed it is the pocket pistol, since after the nerf it is terrible. All other scout secondaries are banned for good reason.
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Wrap Assassin:
15 base + 40 bleed, recharge in 15s. A weaker version of the guillotine but the same argument applies. There should be no "free" damage allowed in a truly competitive game, you should need to do something skillful to do damage and both the guillotine and wrap are not skillful. Ignoring the plea to skill argument, 50dmg on the flank is still usually enough to open it up for some prodding that otherwise would have required coordinated play by more than just the scout on the team.
As for unlocks everything is relatively useless except for the atomizer, basher, and sandman. Atomizer is obviously never going to be unbanned and the same goes for the sandman. (As an aside, the cleaver does an arguably better job than the sandman at securing kills.) With the escape plan change, there really isn't a need for scouts to build uber now and the jumps that you can do with the basher fall into the same problem as the winger, you really can't do them in a fight, they only save time.
Like the secondary slot above, there is a banned weapon that really shouldn't be: the candy cane. The candy cane could drop medium packs and I don't think scouts would run it because of its downside. A pipe or close range rocket is a 1 shot without a buff. Honestly people keep looking for a way to stop the scout dominance that they have right now and forcing them all to run the candy cane would be a pretty effective (and silly) nerf.
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Brass Beast
A heavy that walks away from the point is basically awarding the enemy team the capture, so your purported downside is one that already exists. However, the spin time and almost complete removal of mobility when spun up makes it bad enough that the only way to play with it is to stand still and not move, which effectively turns you into a sentry gun that takes up a spot on your team. Nobody (seriously) complains about sentries so there should be no complaints about this weapon. For an example, if you run brass beast on badlands last and hold on the upper platforms, the enemy team would be able to cap the point before you were able to get to the ground and either rev up to kill or step on the point. Against robots it is great, but against actual humans the movement reduction and spin time are terrible.
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Tide Turner
In 6s worse than the targe, but nonetheless an incredibly frustrating to play against weapon. This is one of those items you will get endless complaints about but nothing that really impacts the game so it will probably fall onto the league admins to make a ruling one way or another.
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Gunslinger
This item is extremely controversial, hell there are even a good number of HL people who want it gone from their format. But like you said, any kind of coordination is easily able to take out a sentry. This is one of the few weapons that I would want to see brand new testing done before being allowed. There are good arguments on both side of the coin and I'd rather not have a season destroyed due to allowing it over a convincing argument. A "forced engie" cup, where every team actually tries (unlike the all unlocks cup), really is the only way I see getting a community acceptable answer on this weapon.
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Panic Attack, Phlog, and Carbine should all be allowed.
Other items that you didn't list but should probably be allowed with little to no testing: Persian Persuader (demo gets no ammo), Fists of Steel, Cozy Camper,
Items that are 70/30 to 50/50 allowed and probably need a bit of testing before allowing: Base jumper, Pomson 6000, and Short Circuit