Eliminating the leaderboard might help. By measuring it as a race, it becomes a race, and now the goal is the metric.
Maybe just have a cool advent calendar thingy like a digital tree that gains an ornament for each day you complete. Each ornament can be themed for each puzzle.
Of course I hope it goes without saying that the creator(s) can do it however they want and we’re nothing but richer for it existing.
> By measuring it as a race, it becomes a race, and now the goal is the metric.
It becomes a race when you start seeing it as a race :) One can just... ignore the leaderboard
That 'digital tree' idea is similar to how AoC has always worked. There's a theme-appropriate ASCII graphic on the problem page that gains color and effects as you complete problems. It's not always a tree, but it was in 2015 (the first year), and in several other years at least one tree is visible. https://adventofcode.com/2015