I have not healed, but as a dps and tank:
excluding buggy Soa.
I find EV and KP normal are about the same,
and also EV and KP HM are about the same also.
more mechanics means less margin of error,
which equates to more difficult fight.
I have tanked them as well, and for the most part i feel that the fights in EV/KP are very simple and more or less tank and spanks. What mechanics they do have, are very simple (especially in 8 man) and can be easily overlooked. The mechanics in EC are not extremely difficult though, there isn't any fail scripts in any of the fights, and the mechanics are more less based around positioning and distance... the two easiest mechanics that can be introduced in a fight.
If they made the mechanics more forgiving/easier in EC or made an in-between raid/FP people would most likely ignore most of the mechanics of the fight and wouldnt progress as better players. With each raid/operation, a raid force should get better.