Mostly agree with you except in two parts:
gold league is a significant mid-level investment, I don't think it should be ignored or grouped with diamond. If modern is going to need constant investment, then silver-> gold is a significant upsize. as is gold -> diamond. Silver -> diamond may seem impossible. Giving smaller goals makes progression feel possible.
IMO there's no need to completely remove the leaderboard itself at lower leagues - people still want to feel competitive. But rewarding with glint instead of DEC or SPS will limit the economic incentive to camp.