1.) The simple answer to your question is: Draw a lot. Not like, 24/7, but a lot. Having a comic is actually a huge help with that, and you will improve over time without even realizing it until you look back at your older stuff.
2.) Impostor syndrome is a real thing and no matter how good you get, you're always going to judge your own work wayyyy more harshly than you do other people's, so just be prepared for that.
3.) As for your art specifically; it really isn't bad at all, you have a strong style and your characters are all very distinct from one another, though I can see why you'd want to move in the direction of some of the examples you posted. Best thing to do is to study artists you like, try replicating some of their drawings or their style to really break down what exactly they're doing that makes it look good (obviously, don't post this stuff as original work). The other best thing to do is use photo reference as much as possible. If you think you know what something looks like--trust me, you don't; look it up. If you're currently not using it much, starting to use reference regularly is a pretty good formula for very quick, noticeable improvement.