The reason you’re great at one-off compositions but can’t put a long-form comic or animation together to save your life isn’t because you’re a lousy artist, it’s because you’re a lousy project manager.
I know that doesn’t sound particularly positive, but you’d be astounded how many artists I’ve run into who are literally unaware that project management is a) a totally separate skill set from being Good At Art, and b) something you actually have to learn – they think that people are just intrinsically good or bad at doing long-form projects and that’s all there is to it.
Correctly identifying what it is that you suck at is the first step to improving!
This also applies to long-form writing.
Oh.