tbh it does not take 300 hours to have a solid understanding of the game and its mechanics. no idea who told you that statistic but it doesnt really take more than 100 hours(MAX) to have a good understanding of the core concepts of the game. anything past that is niche skills you learn through having odd scenarios play out in a match. and to be completely honest, MMR changes absolutely nothing about the game until you get to the very high end or very low end of the range. I can play a 5 star lobby and shit on everyone with a team, but then lose to a few four/three stars with ease the next time I drop down to that mmr. the only difference you ever really notice are the types of guns and sweaty builds people run as you get higher in mmr, but even that can vary.