In my opinion "raid difficulty" is very subjective.

A little before 3.4 hit i was catching up on some of my alt gear in void ark. There was comment and jokes on how void ark was very easy. I pointed out people came in there with averages of 230-240 while the recommended was 175.

When 3.4 hit, some people came back to the game and never did weeping city. I couldn't get the thing done with the duty finder for the first few days while those people were learning the fights.

My opinion is unless you sync the gear you can't really talk about raid difficulty.