Since not all of the Neopets Battledome 1-player difficulty ratings make sense, maybe the In-Depth Battlepedia should give is own ratings based on how difficult they are to beat (ratings could possibly be split into more than one category like how hard they hit and other factors).
how tough they are completely depends on how tough your pet is 0_o
Also weapons sets. Because, say a 1P enemy does mostly earth damage. Get a leaf shield, and they wont hurt you. But a comparitively weaker enemy using fire will kill you in seconds. So it's all relative really.
I can see vernax's point tho - how many 6 icon weapons do they have, what healer they have, if they have any 10+ or 20+ icon weapons or if they have a freezer/t-tear. I agree that any shield can render a fight relativly easy, however I think a generic overview would be nice.
Playing devil's advocate however, I feel that the idb already has comprehensive weapon lists from 1p challengers, I know that I helped many others look into the possible weapon combinations, and as said before everyone has a different idea of hard.