I would say it's pretty vital to the success of the comic to have good art. It tells the audience right away the type of genre they're walking into, it tells you if you're too young/old to be there reading it, and there's a lot of visual language we use in comic making to get abstract ideas across. What I'm looking for in a comic isn't the same as what I look for in standalone illustration either. Mostly because the time scale is just different, webcomics need to be made so fast, while an illustration I can spend several hours on no problem.
And like it depends on the comic, but as a reader, I don't expect for a webcomic author to be spending 2+ hours a panel, and I would hope that they don't. Go ahead and take the short cuts, it's a web comic. I'll admit that occasionally you'll have a humdinger panel that takes about that long, but most should just average less. So when there are issues with perspective or issues with anatomy that are fairly minor, I don't really care, and honestly I read so quickly why would I notice those things unless they were very large?
When drawing errors get in the way of legibility, and aren't editorialized to be appealing to look at, it can be distracting enough to hurt the reader experience. I would change those things, but only when you have the time to do it, and if it's worth doing (like redoing old episodes can be a real sisyphean dilemma.) But honestly every comic you do, you will be better at art than the last one, so if you aren't like at the teir of a top level comic it's fine, we're all learning. You have to keep creating in order to learn how to do it better anyway, so releasing less than perfect work is fine.