Ask much as I liked Wrath of the Lich King, it probably started there. The raids and heroics were much easier, compared to BC and vanilla
no they werent
take off the glasses and look at the mechanics in vanilla raids vs wrath
the difference is night and day
vanilla was only "hard" because it was a buggy mess, there was no clear design or balance among classes at all, gearing was a nightmare (3 drops for a 40 man raid, lol), itemization was garbage, there was very little theorycrafting, addons were not as complex as they are now, etc etc
i mean seriously, look at a fight like 25h arthas compared to literally anything in vanilla
Vanilla is hard in different ways. For one it's far less forgiving. I remember playing as a warrior tank during MoP and WoD and I had so many different "oh shit" buttons I could push if something went wrong, like Shield Wall and Last Stand and stuff, and they were on fairly short cooldowns no more than 5 mins each.
In Vanilla, you have far less wiggle room and mistakes get punished more severely. Compared to mythic anything, vanilla raids will all seem quite simple, but only the super elitists of WoW ever even set foot into mythic anyways.
Vanilla is hard in the same that it's hard to cut a block of wood with a wrench.
Mythic raiding is hard in the same way building a house is hard with every tool available.