I was referring to the fact that you won't know a damned rotation because you'll start off at level 60 with all these moves, and you never leveled the class from the ground up, which would help you have a grasp of how to use all of them in actual combat. Combat experience helps you learn what works and what doesn't, and it's far easier to get it properly if you're leveling up a class.
You're comparing different endgame raids, of which Nidhogg EX is one of the newest. People expect you to at least have a grasp of what's going on since not everybody learns at the same pace, so watching the video lets you know what to expect. But we both know there are people who won't watch the guides, who won't educate themselves...they're the ones that will cause the problems at endgame. The ignorant who refuse to educate themselves beforehand.
Though that's moving beyond the normal boss mechanics I was referring to. Every boss in this game builds off what you've learned from a previous one in some way. Sastasha's boss teaches you that there are mechanics, and failing them will punish you in some way. Tam-Tara's will teach you tether mechanics and dealing with adds during the boss. Copperbell's will teach you how important it is to take out the adds first, for they could be part of a mechanic. Totorak teaches you how to deal with DoTs multiple targets on the boss. Etc Etc. The bosses slowly build your knowledge of mechanics over time, a bunch of mechanics somebody suddenly thrust into endgame from the beginning will not know, and will easily fail.
The bad players will be the ones who go straight to 60 from the getgo with the said item proposed before. We're cutting down on them by having them work their way up. Yes, we'll always have bad players at endgame, but I'd rather have a group of 100 new players work their way up to endgame and have 75 of them end up decent or better, than to have a group of 100 start off at level 60 and only have 15 of them be decent or better.