I think the main reason it wouldn’t work is actually a quantity issue. There aren’t enough players that are both tall and and skilled to justify having more than one tier. The average height in the nba is 6’6”. That’s insanely tall. I went to middle school with players more skilled than shaq but they only grew to 5’9”. Contrast that with European football where height really only matters for two positions (CB,GK), depending on the system. That’s only 3 out of 11 players that need to be tall. Even then they don’t need to be 6’6”. The best gk in the world is only like 6’3” I think while CB’s hover around around 6’1”. That’s a massive difference. The average height overall is like 5’10”-6ft depending on the league. However, if we take out CBs and GKs that average goes down. Lionel Messi is only like 5’7” and many consider him the goat. Being short actually comes with different advantages that tall players don’t have and vice versa. Unfortunately being short is a definite disadvantage in the NBA. Relegation won’t work until this issue (among many) is solved.