Something people don't tell you is that this feeling doesn't really go away. Ever.
I've been published, worked for some pretty big companies, placed in national competitions, I have a decent-sized, growing following and I still regularly feel like "...what if I suck though?". I look at friends I have with thousands or tens of thousands of followers on their comics who tell me my comic is good, and I can't get rid of that little voice in my mind that says things like, "they're just being nice to you, you're not really on their level. Their comics aren't more popular than yours because they've been running longer or because they're in more popular genres, those are just excuses you tell yourself, your comic just isn't that good. The people who hired you picked you because you're cheap, not because you're good."
But then... those people with popular comics, they're dealing with the exact same thing, they're thinking, "my comic isn't good, people are only reading because it has hot boys and tropes in it, oh god, what if my readership is declining? I've put years of work into this, what if people realise it sucks and get bored of it!?" or "What if this is the only good/popular thing I ever make and actually people only liked it for the tropes and won't follow me into my next project because they're not here for my skill at all?"
It's natural to feel that way. I've known people who have done huge work in comics and sustained a career for years who feel terrible imposter syndrome that they're actually a bad artist and some day somebody will have the guts to point it out and everyone will suddenly go "wait, they ARE a bad artist! chuck them out!"
There's no easy solution. Just remember, you're not alone in feeling this way. With art commodified as a "career", it's easy to conflate worthiness and profitability, and Tapas' UI does encourage this with that rather unpleasant little bar that makes people feel like they haven't "made it" until they get to 100 and then 250 subs, but the print industry has a similar thing with "breaking in", where to be a "proper comics artist" you need to have been published, but not just self-published, it has to be a recognised print publisher. It's all pretty toxic. In the end, the main thing is that you can reflect on your progress and feel proud of the improvement, and you can read through your comic and feel like you made an enjoyable read.