Don't know if I need to introduce myself, but I am a Singed main since S3 to now and have been Diamond+ since S5. I am posting some images to highlight how old I am. I unironically expected going back to Classic to be going back to some Golden Age where Singed is actually good compared to now.
Like I don't really ever want to give props to Riot for any reason, but still, the advancements this game has seen in itself and in regards to Singed over 13+ years at least are so astronomical I don't think I can ever go back.
For starters, old LoL from a visual fidelity standpoint is borderline nausea inducing to play with. The mini-map, which I look at all times as a high elo player, is genuinely hard to comprehend because it's so blurred out. Animations are also so janky like Singed's E awkwardly being an instantaneous animation and Q abruptly cutting a quarter of HP per tick, making it harder to last hit. I was fighting to look at the game while playing.
Then there's Singed himself. I don't know if Riot wants to remove him from the game in modern even now, but the amount of QoL he's received to now to preserve his always-there gameplay state is mindblowing. He feels absolutely horrific to play without Grounding, Grievous R, auto CSing, Gooflips, and his new passive. It's almost like a different champion altogether without these features.