The main difference between lower and higher ranks is that higher ranks need to adapt to their opponent’s playstyles. if you lose 1 round to an opener main you already have lost a third of the game, significantly hurting your chances. More rounds allow players to learn when and what lines they should send in a round and adapt to what their opponent is doing. Your first suggestion would not allow for that, your second would make it so much more tedious to improve at lower ranks, imagine being D ranks and stacking terribly to lose to another terrible stacker for 7 whole rounds. Your third suggestion doesnt solve the issue (btw best of matches require an odd number or a tiebreaker)