Top:
Yasuo's repetitive auto q auto trade pattern from outside other melee characters ranges, infinite dashes, ranged cc, and free shield are annoying enough on their own, but getting 100% crit from just 1 and a half items (making his damage from ult into effectively all true damage) put him far past the tipping point.
Tryndamere just ignores the game and forces everything to revolve around him
Sett not needing to even stack his grit to do more true damage with his W than most characters get as magic or physical on lesser range abilities, it basically negates the entire point of his counterplay. On top of that being a tank killer at a point in the game where tanks have already been struggling for 2 years straight is just asinine.
Jungle:

Just the typical smurf champions seen in the role so it shouldn't be surprising. They all take advantage of the shitty early level invades that unorganized teams can't react to, but there's a special place in hell for Ekko jungle players particularly.
Mid:
Yasuo has all the same cancer as his top lane play with his free shield and dashes, but on top of that gets to be immune to characters' entire kits mid thanks to windwall.
Talon is like a corollary to Tryndamere. Where tryndamere ignores the rest of the game and splitpushes 24/7, Talon ignores his own lane after his cheesy level 2 first blood and just picks up free kills with his global threat of one shotting.
Akali nerfs honestly did nothing. She still does twice as much damage level 1 with Q and passive as any other character and still dashes around endlessly in late game fights picking off targets. Now with 60s cooldown ults that do 120 extra base damage for even more cancer!
Bot:

No surprises here. All three are still grossly overtuned in raw damage and utility, and all three snowball out of control more than any other character in the role.
Support:
(and collectively all APC "supports")
The spooky water hook brothers both make lane phase incredibly boring with bush camping to fish for cheesy kills, which are practically guaranteed if they land a hook thanks to their base damage and the ensuing free autos they grant their ADC.
Mage supports as a whole, though highlighting Brand since his awful AP ratios and 0 trading potential without giving up CS practically ask him to be played in the role. The radius and cast time of his W actually make the ability impossible to dodge if he just casts it centered on an opponent with less than 400 MS or a dash, while dealing ridiculous damage at very low risk (since he doesn't have to worry about giving up W's waveclear power).