Took me 65 games to go from plat 2 to masters this split. Every take here you read here likely to be garbage (sorry, it's the truth).
Apexuniversity is only marginally better than the main sub (obviously an opinion).
Things you need to get to masters: Aim, Positioning. Nothing else. That's what you NEED. Believe it or not many masters players end up hardstuck 10k and are just as brain dead as many D4 players - but at least some of these guys continuously win their ones.
What I think you need.
Aim. Self explanatory. Learn recoil smoothing, recoil control, hip firing is usually the way to go for anything close range with any gun.
positioning. I play Wraith/Caustic mainly. I play the two legends near identically as far as positioning goes. My playstyle revolves around NEVER giving the enemy the opening damage opportunity. Killing in apex is a numbers game. Assume both teams are 3x purple, that's 600hp vs. 600 HP. It's a catastrophic disadvantage to begin with 500hp vs 600hp. Wait for the enemy to fuck up their positioning and you'll have an in. This isn't a rule, 3rd parties, RNG, etc can throw all this out the window and at some point you just have to be better. That said, not taking damage is just as important as giving damage.
mechanics. I play controller and I notice so many players limit themselves because they don't think controller is "supposed" to have good mechanics. You should be able to JUMP, open up a death box, shield swap, loot a few items before you even touch the ground again. Or learn basic movement techniques. Super glide, super jump, wall bounce, mantle animation cancel, air strafe and super air strafe.
This is my last clip dump from the first week of the season. You can get a small glimpse of where I'm at mechanically.
Good luck!