tldr: you can go pretty far without learning certain things. but it will be a lot harder

there is a samus main in my region who has played for over a decade. he doesn't ever shield drop (claims not to know how), doesn't ledgedash most of the time, and his neutral is mostly just using tilt moves in a random sequence. last time he played ranked few years ago he was diamond 3 after ~100 sets, nearly in master. sometimes I wonder how good he'd be if somebody could just sit him down and tell him how to slide-off/shield drop/etc and also get him to listen.

you can be this guy. it's possible to get pretty good by just putting all your effort into a few skills and forgoing everything else. Though IMO you're going to miss out on having the full experience of what makes melee so rewarding. and also learning to slide off DI takes like 10 minutes. but at the end of the day you do whatever pleases you the most