My reasons for saying that is because IMO scholar and obviously by some connection WHM, are the only class you cant just run into and attack things and expect to succeed. Anyone who has someone on their team who was dps but switched to healer because no one else had one is the perfect testament to this. Play ing healer in pvp even marginally well requires a thorough understanding of your pve AND pvp skills. It's not like bard where you can survive without enliven/blast shot/far shot etc. you functionally cannot operate as a healer in pvp unless you know apropriate timing for this like attunement and equanimity. The fact you are a healer instantly makes you target number 1 which is something lets say a dragoon or a warrior doesn't have to worry about. All of your skills (with the exception of regen lustrate and benediction) are interruptible and guess what, a healer unable to use skills makes them 100% useless. Aside from that there is the added pressure of being the deciding factor as to whether or not a flag gets captured, kill a team's healer and watch how quickly the rest of them go down. That is a lot of responsibility to put on a couple of players. All in all I say scholar is the most difficult class to play because it requires that you don't **** up and have a constant awareness of what is going on in the fight and what skills you have available to you/on CD.
If your a monk you can pretty much just run in and attack things and still be mildly efficient, as a paladin you can run in and attack things and be mildly efficient, if your a scholar and you run in and just start trying to heal your going to find yourself frustrated for the 10 seconds before your dead because you thought surecast was a useless skill and didn't put it on your hotbar. Also look at wolves den, there isn't even a learning curve for healers there so much as a steep cliff drop off. For a healer in wolves den you dead within 10-20 seconds if you dont know what you are doing and a dead healer means a dead team in WD.
The only reason i would rank scholar slightly harder then WHM is the lack of CC abilities with blizzard 2 being the only real option and that requires giving up a CC slot.