I find jayce to be a poor champion for these reasons I will now outline.

he is essentially the culmination of lee sin and teemo into one ungodly mess of a champion. he was designed to be an ad caster, a poke based champion for the mid and sometimes top, and in either case he leaves several things to be desired. he's far too squishy for a top laner and he falls off in damage unless he goes full burst, however he is entirely obnoxious for the laning phase because he needs to snowball hard in order to be of any use to his team. his teamfighting is atrocious under most cases and he relies on jumping and bursting one or maybe two people if they were dumb enough to stand close together at low hp.

for mid his poke and only skillshot is unreliable in such close quarters and the cooldowns too long and telegraphed to be able to compete with his laner. the main reason his cooldowns are so long is because he does have 6 of them however half of them are utility and/or require going all in in order to be put to full use, which, as a squishy midlaner with a singular gapcloser and no good outplay mechanics like many assassins he's pretty much toast.

in general his champion hitbox is just janky as hell and makes landing certain skillshots on him hard such as a nida spear, mainly I think because of his hammer but I've thrown things straight through him and had those moments of "oh come on! that hit him!" that just made laning vs him even more frustrating than it needed to be.

overall if yasuo were a caster, he'd be it. I dislike seeing him on my team or the enemy team because I don't know if we're going to get really unlucky and the top laner can't do shit and he pushes all 3 tower in under 20 minutes and proceeds to wipe our faces with his ad scalings or he'll fall behind and be useless except to be a discount lee sin who never stops split pushing and dying.