I don't know why people assume the top end of the game should be easy. No game I have ever played and enjoyed was too easy at the end...overcoming the challenge is half the enjoyment! And this must be a recent phenomenon since I hear BC raiding was not easy pre-3.0.2 and everything post-Karazhan is actually pretty tough post-nerf. Did everyone forget in the first 5 months of WOTLK that Naxx was basically a placeholder? I mean not only did everyone know the fight strategies, but it was deliberately made easy.
It's like Jedoga in H-OK. I came to the conclusion that the most important thing was getting the add down before the sacrifice or else I couldn't keep up with healing w/o blowing my only CD. So instead of my normal strategy in such times where I would gain some mana for the duration, I made the decision to offer my weak DPS during that few seconds, which put us over the top. We learned and adapted to beat the boss.
Additional examples: this morning we cleared the first boss event on AN on the fourth try because I died during the third set of mobs, put up some big heals and a couple HoT's on the tank during my spirit phase, then busted my ass back into the instance, where I got there just in time to put Guardian Spirit on the tank and recover to beat the boss. Clapp was whispering me after the fight and was clearly impressed with my "recovery" on that fight. Knowledge from previous encounters with that awful boss event led me to the knowledge I used to be a good player in that situation this morning.
Also in H-OK, I had to make a split decision on whether to use one of my last 2 mana pots on our attempt at Herald Volasj when we lost Caz and the other 2 DPS (one of which was a Shammy) at around 40% and before the second Insanity. I had about 3 minutes left on the CD for Shadowfiend and we were going to wipe without the mana pot as I was OOM. I knew from previous experience that we could elongate the Insanity phase by simply not killing the healer in one of the other person's insanity, and thankfully the tank knew this as well and was just doing enough damage to insane Ekat to break even. So we recovered about half our mana bars and made it within 15 seconds of Shadowfiend coming active again before we finished the insanity phase and proceeded to down the boss easily (I think the Shammy battle rezzed themselves going into the final phase as well, but not 100% sure on that mechanic). We overcame losing all 3 DPS which is amazing, but I had to make a split decision on the mana pot and I made the correct decision that we could recover from that position rather than conceding defeat.
So maybe I'm an above-average player (I don't like to think so), but I learn from my experiences in game and adapt my play to be better off. I make informed rational decisions when I can. Perhaps this is why I'm a Holy Priest healer, because you really have to think about when you will use the tools given to you.
Like the new Holy Hymn which is on a 10 minute CD but gives you 12 medium sized heals on the party over 9 seconds. I still am figuring out when I should use that new ability, and will be better off once I do figure out the best time to use it. Right now, I have no clue.