The actual writing from a lot of the golden age and New Wave sci-fi authors is... OK at best, with a few exceptions (Bradbury's distinctively poetic and dreamlike prose, for example). Tons of modern sci-fi authors write stories with more literary merit, better clarity, better-conveyed action, more believable characters and dialog, and so on. The improvements there are really obvious when reading, say, an early 70s The Hugo Winners or collections of 1950s stories, and then a 90s The New Hugo Winners.

Whether their ideas and worlds stand up to Asimov and company, or happen to be appealing to a particular reader, is another matter, but the command of writing itself is overall better, I'd say. I don't think a modern author would have much luck getting novels or stories in major magazines published with Asimov-tier dialog & characterization, for example.

Plus those eras were full of tons of garbage, in addition to what we remember. New Wave (60s and 70s) in particular tended to some very special interests that I don't think have held up too well, with some exceptions. A lot of that era's stories are very in love with sex & drugs and not in a way that really translates into a good tale. Most of those aren't exactly well-beloved these days.

On the flip side, there are definitely some modern sci-fi authors that are among the most famous but have some serious problems putting together an entirely good novel. I'll refrain from naming names but among them is maybe the only author whose book has ever made me mad at them for wasting such a good idea, setting, and opening, by just having no damn follow-through and getting super lazy in the last 1/3 or so. They're probably a top-5 sci fi name, among active authors today. But I stand by the overall quality level being notably higher on at least some dimensions, and it's even true for that guy.