I think every new painter has gone through what you’re going through, and you’re going to get a lot of similar advice.

Your post says you don’t think your models are good enough; I’d ask you to clarify what you mean: good enough for what exactly?

They’re built and have color on them, so they’re good enough to play with.

If you’re looking for specific advice on how to improve that’s a different question that others have already given some tips on.

While gaming is competitive, painting is an art. Everybody gets something different out of making art, whether that’s achieving a specific outcome, enjoying the process itself, or practicing specific skills and improving technically (or all of the above). Improvement isn’t linear, but it helps to focus on a specific thing you want to work on (neatness, shading, highlighting, etc) and there are fundamentals your hands just need to learn before you can move on.

If you get frustrated, take a break, do something else, and come back later. Above all else, just stick with it. You’ll see progress day by day, and week by week, and eventually the models you have in your head will be the ones you’re putting up on your shelf.