Sorry but this is very *****ic. Half of this is not even true or incomplete and very vague.
Already the first sentence: Hpal the easiest healer? Really? In the sense of rotation, every healer is easy, since most spam not more than 1-2 buttons, with the only difference that hpal needs to manage cds like sacred shield and especially beacon, and 1 bad cd usage or beacon refresh and the tank dies, making it the least forgiving healer, really not for beginners.
The absolutely easiest healer for starters would probably be restoshaman or discpriest, and discpriest also only if you understand the sense of the spec. i've seen disc priest shield some people and then spam flash heal, please don't do that.
the rshaman description is very vague. the whole sense of rshamans is that theyre versatile and that they can burst aoe heal to stablize huge damage spikes onto the raid, otherwise a restodruid or holypriest will always outheal shamans in the long run on consistent healing.
the rdruid revitalize doesnt only restore mana, it also restores energy, rune power, rage etc, which not only increases the mana but also the dps.
you forgot that discpriest basically gives a (renewed hope) 3% reduction to all damage permanently, and that disc priests are also needed in every 25man raid. and discpriests are useful in EVERY fight. sometimes more, sometimes less, but in every fight where somebody could die to mechanics (= every fight) they are useful due to shields preventing oneshots and deaths.
hpriest isnt complicated, it just has the most buttons. and there is 3 ways to play it, you forgot the hybrid spec, which is actually even the most common one, combining renew talents and glyphs with serendipity and going for about 800-900 haste.
the biggest skillcap probably has hpriest tho just because they have a lot of potential and are so different in the ways you can play them.