Most clears in a short amount of time = Easy
Small amount of clears in a long amount of time = Hard

Maybe also use the ratings as a divider to have a smaller number, there could be multiple ranges that categorize the result you get to determine what is the difficulty of the level.
The smaller the result is the harder the level is pretty much, and the result is the average of clears every day or something

I do think multipble filters for difficulty would be needed because the time thing dosent take into account speedrunning which judging by how ratings are if a speedrunner got a good time on a level with few clears it could be bumped up a buncha spots on that filter