I dont think anyone is really saying there is a "problem" or, if there is, i certainly dont agree with them. However i think a small section of the classic community set themselves up for disappointment, and in some situations, a bit of general mockery. Many of us (i would like to think the majority) knew how low the difficulty was compared to modern wow, and were actually looking forward to it. The joy of the current setup with both classic and retail running together is, if you want a challenge, retail is there for you. If you prefer a more social and very simplistic version of the game, that exists as well! I think thats a fantastic thing.
The difficulty and requirements of retails harder content mean it can be quite draining on higher end players, so for many, classic is a great opportunity to still raid, but without any of the challenges presented by harder content. Like i said, many, if not most, knew this was the case long ahead of the launch of classic, and got exactly what we expected. However there was a very vocal minority who suggested classics content would be a challenge even for heroic/mythic raiders, and now that they have egg on their face, there is a level of enjoyment for some watching them squirm and twist in discomfort as the truth comes out.
Most of those players gave up fighting the truth almost immediately, however some stuck to their guns and simply went with excuses, and some amazing attempts at revisionist history. The goalposts have now clearly been shifted to the next raid, and when that falls over in a matter of hours, and casual raid guilds have it cleared week 1, the goalposts will shift again until eventually we reach naxx. At that point, the inevitable will happen:
"no one EVER said vanilla raids were going to be hard, but you just wait for BC! its going to destroy guilds!"
tl;dr - Its not a "problem" so much as it is an interesting discussion point.
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No drama at all, just making sure you didnt think i was the loony who thinks vanilla raids are as hard as current Mythic.