You absolutely slaughter a Singed and most other melee champs early game because you are playing an early game champion that gets outscaled by Singed with 2 items ?
Singed is not supposed to win match ups, him winning match ups was a product of him being extremely overpowered.
He's a nuisance that goes around interrupting teamfights, pushing waves, getting people to waste their time chasing him, messing with the jungler and so on.
You think Singed should be winning laning phase ? Then why the F would anyone pick anything other than Singed ?
If you get ahead as Singed you go into a teamfight 1v5, spread your miasma, activate righteous glory, flip their ADC and basically win the game with there being NO counterplay since he is so tanky and gets so many free stats from his ultimate
There are no Renektons in master besides one in Korea who is challenger and that's because in Korea junglers know how to gank a Renekton lane and carry him.
Singed works well with Aftershock, grasp, aery for damage, they are all good on him and he can just bypass the entire laning phase and be a threat no matter what