I agree with everything you've said. There are learning opportunities everywhere. Part of being a professional is having a interest in those topics and a proclivity to integrate them. And you're absolutely right - if you're out of your depth, you need to learn when to scale back.
I think we might be talking about two different groups of people, though. There are comic creators who WANT to be professional and fail at even the most rudimentary customer service. Then there are those who are just kind of dicking around, stumble onto a formula for content that works and kind of get swept up into producing books, selling ad space, etc. because they get the impression that's what they're supposed to do.
If you want to be treated like a professional, you absolutely have to act like one. But I think for the majority of webcomic creators, the thought doesn't even enter their minds.
I mean, look at the number of creators who are living on their work - you could probably count them on your hands. Those who turn a mild profit like I managed to for a few years are maybe a couple dozen more. The majority of webcomics are either just making enough in ad revenue to cover hosting or they're throwing money down a hole (willingly, I'm certain, because they love doing it.)