People have short memories, many boss fights are incredibly difficult the first few attempts but become pretty easy as gear and experience improves and everyone learns the fight.
Any time someone dares to suggest a boss might be hard you get flooded by comments by how easy it is and how you must be a noob. That's just noise to me and I ignore it.
A couple I remember from Wow, we were a pretty casual guild and not serious raiders so we often struggled with things others had long since cleared. Deathwing and the Lich King come to mind, both easy fights with an experienced, geared, coordinated raid group but absolute nightmares for a bunch of amateurs learning for the first time.
The safety dance in Naxx was all but impossible for us as well - but not becasue of it's difficulty. Try timing things like that when everybodys latency is in the 200-300ms range, we are an Aussie/ Kiwi guild and that was normal back then. Certainly added an extra level of difficulty.