I mean, i´d argue that on hit varus overlaps severely with kog.
Kayle and Xayah overlap a fair bit as well, around average ranges, DPS, survival ults.
And crit varus overlaps a ton with cait and jinx.
.....A number of marksmen are just kinda similar to eachother in several ways, as are the tanks.
Lux and ziggs have a some points of similarity in terms of how they play, poking around, ensuring enemy wont dodge then ulti for a finisher.
Xerath and vel feel pretty similar too, just like someone switched the basic abilities around a bit and modified them then changed the effects of the ults but kept the rooting mechanic.
Jayce and gnar have some points that are rather same too, poke in ranged form then go all in in melee when confident, back off with some CC/mobility if it fails.'
Yi&Tryndamere.......run in, basic attack stuff and use the dash whenever you feel like, one pops ulti first and the other midway and both keeps hitting until they either win or lose.
Ekko , Ahri and sivir all basically have the same Q with some differences in number, appearances and a minor special mechanic here or there like the return true damage on Ahri´s Q then we also have cassio and karthus kinda suffer from the same deal ......syndra too i guess.
In effect Shyv and wukong have the same passives pretty much.
Nunu W and Sion ulti? One isnt unstoppable and the other is.
Riven and Aatrox are also very similar, difference is just that riven have this animation cancelling deal that was originally a bunch of bugs which later got officially adopted.......but overall aatrox Q is like riven Q+W combined with some restrictions.
E´s are basically the same but Aatrox gets a
sustain passive instead of a activated barrier and 2 charges of the dash.
Both of their ults are just fat stat buffs altho riven can activate hers again for a execute while Aatrox revives if killed.
I´d make a case for morg and lux too, light/dark binding, the shields, instant/delayed damage AOE circle.....only big difference is the ults.
What am i going for here?
OP you might as well drop the idea of true uniqueness,,,,,,its probably already not possible with the 141 champions we have. .