They have actually learned their lessons as of today. In 10M normal Mogu'shan the tanks have the brain thinking of handling the bosses. You got three bosses that you need to juggle to make sure the right one overloads. Which is quite interesting.
Then you got The troll boss where you rely on DPS and a healer to go into spirit world and handle adds while tank keep boss busy. So in that aspect they learned.
But it is too simple for let us say knowing the tactics from just going LFR.
You don't necessarily need to make raids harder to make them more entertaining, you simply need to add more mechanics into the fight, like you said. So every class get something to do each fight so it doesn't become that only one class have to think on what is going on.
To jsut add extra mechanics into let us say a normal fight in comparison to a LFR fight doesn't necessarily mean it gets harder/easier. Let us take my Tsulong example.
Let us say you get that sort of meter where your fear grows during the night when you fight Tsulong. Since hitting the boss radiates fear into the hearts of the champions trying to help him. Once you reach maximum you get Feared for well, long time. If you click the button just above the fear meter, you spawn a mob looks exactly like you. And you kill it. Meaning you need to build a strategy. Let one dps click early, then the next in a cycle, it becomes a lil harder in form of coordinating, but it gives all classes something to think about more then keeping the tank up and dps on the boss during night time. And between the breaths, the tanks have to spawn their stuff and kill it. It doesn't even need to be hard mob. Just something htat makes the player turn away from nuking at the boss to prevent a long CC fear. That is not able to escape through trinkets and such.
Such stuff can just simple be added to the boss in Normal. And voila you got a difference between LFR and Normal and the casual gamer and the normal gamer suddenly get something to surprise them, a small obstacle to jump over that just takes one whipe to understand, then it is back and Refining the strategy.
Currently Blizz have learned a lil of their lessons but it is still mostly like this :
Either tanks have to keep something in track. Like juggling bosses.
Or dps have to run around kill adds while tanks does nothing more than nuking and building threat against a boss.
That is why I like being a Tank, I get to be in the action and that doesn't bore me out, being a dps would surely bore me out and you got more pressure on having to DPS correctly. Which is easy to learn or just spam tons of buttons and CD's. Which isn't really hard :P