I don't think this is true...yeah getting 40 people online was difficult and in some cases half the battle, but the fights in general were pretty difficult. The bosses in vanilla were not as "complex" because the engine wasn't originally designed to do a lot of the scripted events that the engine is capable of doing now.
That being said, you gotta remember that Blizzard has implemented a tremendous amount of API enhancements which has increased the number of mods as well as their complexity. We have mods for everything now a days, each encounter is updated with DBM so you hardly have to think during a fight...you have a threat meter that keeps you from pulling aggro...shit you have mods that practically heal the raid for you.
Also, it's very easy to obtain preliminary gear before stepping into raiding instances. I'm sure you all remember that poor tank "decked" out in Valor hahaha...of course MC got a lot of easier once the raid was geared but man was it difficult without that gear. It seems that I can do heroic dungeons (which are a joke) for 2 weeks at minimum and have enough gear to cake walk into Naxx.
All I'm saying is, raids in WotLK are undeniably easier than Vanilla WoW, and that isn't always a bad thing...it caters to a totally different crowd. I thought this was all solved by introducing heroic mode though, if you thought the instance was too hard then you switched to standard mode.
TL;DR
Two Options
A.) Stop being a baby back bitch and improve your skills.
B.) Switch to standard mode of the dungeon.