In fairness to Sid, he was encouraged by Malcolm McLaren (band manager) not to improve as a musician. Sid improved his play over the course of his time in the band, but their incompotent manager decided the future lied in making Sid Vicious famous for being a professional trainwreck instead of a rock musician.
You gotta keep in mind the London punk scene back then was different from the one in America during the 70s. US punk bands still prioritized musical ability & live show performance first, while in England it was more of a political movement of disaffected youth rising up in anger to be as harsh, unrehearsed, and ugly as possible. British punk was always about something else entirely in the 70s. It was viewed as a means to an end, not as a new musical genre to be expanded & improved upon as a new artform itself, the way it was treated in the US.
The last thing I'll say on it was that according to the people on the NYC punk scene in 1978 when Sid was performing as a solo act....... he was actually pretty good. He wasn't panned & rejected the way the movie portrayed him. He had a couple shows where he got a little too high or drunk beforehand, but he realized it was a liability so he never did it again and was always there on time prepared to play. There was never a time where someone had to go rouse him from his nods to turn up for a gig he'd already forgotten about. Or once he got there, he was already so wasted he couldn't even stand up straight or speak plainly. That never happened. Not because he was serious about his career necessarily, but because he needed the money to fund his drug addiction, and he knew he wouldn't get paid if he was as horrible as the movie presented him.
According to the people who worked as booking agents on the NYC punk scene at the time, they never stopped booking Sid. They stopped booking Nancy. Nancy was poison to these shows. Sid would draw huge crowds but Nancy would repel them over the course of the night with her bullshit.