It is commonly claimed that if you make it to ‘level N’ in your mathematics education you will only remember level n − 1 or level n-2 longterm. Obviously there is no canonical way to split knowlege into levels. But one could imagine a chain like:

1) Algebra

2) Calculus (think AP calc in the USA)

3) Linear Algebra and Multi-variable Calculus

4) Basic ‘Analysis’ (roughly proofs of things in Calculus)

5) Measure Theory

6) Advanced Analysis topic X (ex Evan’s Partial Differential Equations)

This theory roughly fits my experience.

I would have a lot of trust in a vote. I seriously doubt we as a community would agree on a set of knower I would trust. Also some similar ideas have been tried and went horribly in at least some cases (ex the alumni dispute resolution council system). It is much harder for bad actors to subvert a vote than to subvert a small number of people.