That's a well known accepted fact, even amongst the people who frequent the forums that create these charts. Of course it isn't accurate; anyone who has attempted bosses from HMag and up should recognize that theoretical damage means nothing. If someone looks at a DPM chart and says yep, Bishop's an awful class because it's dead last on this chart, that person probably hasn't actually played the game.
Trying to measure DPM against actual bosses isn't that feasible either - boss pattern isn't static. Chaos Vellum cycles through some pretty reliable patterns but it's not exactly the same every time you fight the boss, and that unreliability makes it difficult to pull meaningful numbers out of it. I mean, I like the idea - there are some players who have uploaded things like minimum damage Cvell runs or low range boss runs - but it just isn't as measurable as theoretical dummy DPM.
and 32 others. 