could someone provide some specific quantifiers as to what certain difficulty ratings are? like, is it how hard a level was for me to beat? is it how hard a level is in relation to other benchmark levels? if so, what are those benchmarks? i'm just really confused

The rating of it could be how difficult the level was when you played it. That could mean anything to you, maybe it's how annoying the level was to play or maybe how much technical skill it took for you to beat it, It's all subjective, dw about it too much.