I disagree with OP.
Yeah, mechanics were easier back then (I started raiding with ICC, where the assumption still applied for most bosses).
But what we have now is far more complex than just learn boss and you're good to go.
My guild just now started with mythic elisande. You need to do so much kicking, moving (both, melee and ranges, but ranges more), soaking orbs, killing adds at the right time, so rings don't screw your raid, all while maximizing your DPS/HPS on the boss to get it into the next phase.
It kinda shifted to knowing what you have to do in certain situations, while still performing as good as possible, adapting and pulling your weight.