Am I missing something (Semi-experienced player)

Hi all, not sure if this sub is the proper one to ask for help, but here goes anyway:

I've been trying out multiple campaigns as various (what I think is) easy-for-beginners countries. Muscovy, France, Ottomans, Poland. Unfortunately, even though I have almost 700 hours in the game, I'm still quite terrible. Almost all of my campaigns have ended with my military slowly becoming more and more unable to compete with the other major powers. (Oddly though, my military tech is equal to the rest of the world and the battles are hugely outnumbered in my favor + have a decent general, but I still lose them terribly). I'm not really sure what I'm doing wrong, because I'm (mostly) able to compete with the other nations technologically, and have pretty decent income. What am I missing? Is my battle strategy just terrible?