I don’t know the answers so any suggestion I make is just thinking out loud . . .
I do believe that pressure is a factor late in the game but a minor factor for the bulk of the game.
Shooting 50, 100, 200, 1000 free throws in a row in practice will not help shooting during a game and it’s not because of pressure. In my opinion free throw shooting is difficult because of constant variations in a player’s stamina and various fazes of fatigue.
Standing and shooting in practice for 50 attempts allows you to start compensating for fatigue. In a game, they don't give you 50 chances at the free throw line, they give you 1, 2 sometimes 3 shots.
I do think repetition in practice is key but perhaps the reps should come 2 shots at a time after running back and forth down the court and lifting weights while they run.
jmo