One system: head-to-head competition produces the rating, and the rating gives practice a reason to continue. Competition is the retention engine, on purpose.
Neither player sees the other's progress until the challenge ends, so you are playing against the problem rather than the scoreboard. Recognition under time pressure is a different skill from recognition at leisure, and it is the one that matters in a rehearsal. Results feed an ELO-based ranking.
Ranked tiers based on ELO and consistency, with visible progression and regional representation. Not a streak, not points for showing up. A number that means something because everyone is measured the same way.