Hey Ozone! I just checked out your work, and it looks like you're doing VERY well for the amount of time that you've been posting already! DEFINITELY don't give up. You seem to be on the right track.
I think the types of series you're thinking of usually have built in follower bases for the artist. Also, sometimes people just get very lucky and accidentally stumble into a niche that no one really knew existed.
Just keep hanging on, improving, and putting out pages. I think you'll do well for yourself : D
Tangentially, we definitely all feel that way sometimes. (Heck, I beat myself up about my work every other week.) I think it helps to look at the earlier work of people we already admire, and compare it to their most recent stuff. A few authors and creators I look up to weren't that great when they first started out, and you can bet they weren't runaway hits on their first project. It's the fact that they kept going that really matters, though! We're only going to improve from here. Just keep at it!