There is 0 chance that Cata raids were easier than BC raids, especially the launch stuff
Rag and then Spine is the roughest 1-2 punch in back to back raid tiers ever. And T14 was grueling because the average boss difficulty was so high. Most raids have a lot of REALLY easy bosses and then 1-2 hard ones. T14 had no 'extreme hardest boss ever' boss, but it had a ton of very difficult ones. Nef, Alakir, Conclave, Chogall, Ascendant Council, Sinestra...that stuff was no joke. Nothing in the 'many hundred attempts' range, but all of those bosses were ~100 attempt bosses for the average guild. Then Rag is what I consider the hardest boss of all time (besides broken shit), and Spine was just ridiculous hard prior to the nerfs too. I will say the rest of those zones were both pretty easy though (Baleroc was fun the first week but they nerfed him really quickly).
BC had the backwards design of the hardest non-sunwell bosses being Vashj and Kael, two that you had to kill prior to doing the other half of the expansion. So basically, you kill a bunch of midrange T5 bosses, two hard end bosses, and then steamroll BT and Hyjal. VERY few of those T6 bosses took even my completely midrange average guild more than a couple nights. Really only M'uru and KJ were super hard that expac (and yes, they were very hard, but still).