Light level isn't everything. The same enemy at the same light level can have different number of hit points, varying levels of aggressiveness, mobility, accuracy and probably also weapon damage (though simply shooting more and more accurately is a large part of it). There's varying difficulty in different activities (plain old patrol probably being easiest) that isn't really advertised anywhere. Some missions are _substantially_ more difficult, typically the special ones associated with exotic quests. E.g. for some reason I have no trouble running 920 Ordeal Nightfalls, but if I load up a legacy Nightfall that's supposed to be 820, even regular psions kick my teeth in... Light level scaling comes ON TOP of that, and that maxes out at some point (100 levels above, or was it 50? They keep changing it). So basically a mission that is supposed to be super hard will be slightly easier with high light but still hard.