Why should I play Karthus?

half salt/half genuine question, i'm kinda pissed after the game i just got off of

as it currently is what reason do I have to re-learn Karthus? he seems like the worst DPS/carry mage besides Azir who's gonna be buffed or changed soon. I hate crutch mages that depend on Rylai's to function and it's starting to feel like he needs it more and more with how mobile the game is getting

I could pick Ryze and nuke people a lot harder with astronomically less effort and have hard CC. If I wanted just pure DPS I could lock in Cassiopeia and have better team utility in W and R and better/more reliable single target DPS. Azir is loads safer and has tons of options for playmaking power. Aurelion Sol is one of those shitty champs that need Rylai's to actually matter (why i stopped playing him, too), but he's got hard CC and self-peel, and he can do cross-map initiates like nobody's business.

starting to feel like the only thing Karthus gets to do is try to find a good spot to suicide into.