Drawing with a tablet and drawing on paper are pretty different skills, like sculpting with clay and sculpting with stone. You might wind up with a similar thing in the end but the techniques you employ are totally different. Even if you draw well on paper you pretty much need to re-learn drawing now that you have a different medium to work with.
That said the fundamentals of anatomy are universal and will help you with any aspect of objective art involving things that have anatomy (probably won't help too much with landscapes and non-objective abstraction etc.) and if your intent is to draw people, cartoon or not, it is important to learn, but there is no reason you can't learn anatomy on a tablet or even with a mouse, imo.
Regardless, the key is practice and study. Do those and you'll see marked improvement.