EDIT: I'm spending more time clarifying my argument than I'm able to spend exchanging opposing opinions on the merit of my hypothesis (which is just that, a hypothesis). I'm not saying mechanics nowadays are "easier", because there are different types of difficulty. I'm not saying Blizzard bases raids on LFR. I'm going to try and TL;Dr clarify here as much as possible. But honestly, you should read my points to understand the full of them.
LFR is something blizzard knows it has to account for at some point when they design fights. If Tempest Keep was being released nowadays, they may radically change the fight because (among other reasons irrelevent to this conversation) in its current form Kaelthas wouldn't be doable even in a washed-down version. Or more specifically, wouldn't be doable on a RELIABLY CONSISTENT basis. Therefore the regular version would pay for those changes, even if they added other 'equally hard' mechanics to the fight. The thinking, creative mechanics would be removed. The on-your-feet planning mechanics wouldn't be the same, because those aren't reducible.
I was recollecting how alot of normal (and heroic, although to a much lesser extent) mechanics seem 'washed down' as of late. Iconic one or two tank fights with everyone performing their cookie cutter roles for the most part save for timed use of raid cool downs and the occasional major movement obstacle. But nothing 'outside the box' in terms of role fulfillment.
Its difficult to talk about abstract concepts like 'outside the box' mechanics without being pidgeon-holed into saying I want 'new' mechanics or 'hard' mechanics. I think examples might serve to make my point a little clearer. Executus, Onyxia, 4HM, Kaelthas, Illidari Council, Thaddius, Faction Champions, Heroic Anub, 10m Nefarian, 10m Heroic Conclave. I'm sure there's alot more I'm missing. I guess the best way to describe it is 'major multi-tasking fights' that either have large scale use of cc; dedicated non-tank kiting; or creative use of tank switching and rationing adds; or other combinations thereof. Guilds had to be creative when approaching these fights, at least to a little degree, even if they read strategies and guides telling them a framework of what to do. You needed cooperation and teamwork on another level.
And you can't simplify these kinds of fights for a raid finder environment without completely destroying the fundamental nature of the fights. Picture Lich King in raid finder. How you going to get defile not spread to the entire platform? Change its spread speed to be so slow that the entire raid stacked on it takes the whole fight to spread it? That's not the nature of defile, that's a completely different mechanic altogether. Picture 10man Nefarian, and I say 10man because those guilds didn't have the option to 3 tank it, and neither would a raid-finder group with only 2 set tanks. How would you handle the adds in p1? How could you possibly just 'simplify' the mechanic? Hope you have a mage and/or hunter who knew how to kite beforehand? Nerf the adds' damage so pitifully low they could be ignored outright? Then that becomes a different fight altogether.
Minimal use of cc on heroic will of the emperor (even normal will was a cinch to do with absolutely no cc whatsoever) and wind lord, some exotic raid movement on garalon, and from what I've heard and read some unusually in-depth kiting mechanics in heroic sha. But that's in, and even those mechanics either don't exist or can be ignored on normal mode without too much difficulty. Going back to cata in DS and FL seen even less of this except for P4 ragnaros.
Raid Finder is potentially forcing non-comprisingly strict raid roles into the design mindset for encounters. And I'm not saying this in the usual forum snowball effect 'end of the world' conspiracy theory way. Its subtle, and I very well could be completely off base, but something feels homogenized about a trend in raid mechanics that does seem to be getting more noticeable each tier.
I'm honestly not the kind of person who just wants things to blame. I honestly like, on paper, the presence of raid finder because it means I won't be as likely to see nerfs to normal/heroic content. I just feel there's less room for creative brainstorming/solutions and more generic concepts of what a tank, healer, and dps are supposed to do in a fight now than there have been before. And LFR's requirement of pre-selected roles could have legitimately influenced that.