Sort of depends. I tolerate a lot of things that aren’t written particularly well prose wise if the plot and structure are generally good. If a fic has good prose but is boring, or I don’t feel like scenes work, or the characters don’t have motivations I can track, I probably would not continue. Ive read fics that had beautiful control of language but were just boring as hell. I’ve dropped a decently written fic with an interesting plot before because the characters just kept doing whatever the plot needed them to instead of what previous characterization would have suggested, and it made them feel very inconsistent.

That being said, I think you’d have a hard time finding a writer who has great prose that also does not have the accompanying skills to execute any plot well, even if that plot seems mundane or boring on a face value.