Yes, FvS and Clerics should be OP, why? Already in PuGs the last spot to fill in a group is the healer, yes if you are lucky enough to be in a well organised guild maybe you have healers for your raids and elite runs but when it comes to the PuG scene it is quite a different story.
I mean Devs just log into a server and you will see that there will be a few PuGs with the last spot waiting to be filled by a healer.
Having played healers to level 20 with most of my runs with PuG groups I can tell you it can get quite stressful and you have to be on top of your game throughout the quest especially during raids or you could potentially lead the group to wiping (yes I know with a good group this may not always be case but in a PuG raid/run the healer has significantly more responsibility).
You also spend alot more in game plat on scrolls/mana pots then most other classes.
Now because of these reasons my main is no longer a FvS (although I do have an alt level 20 fvs). That being said I really don't mind if FvS/Cleric are more OP than other classes, make blade barrier/implosion a little more powerful, give them more sp, I don't mind how just make players want to play divines. I really don't think the overwhelming majority of players want to play a divine to be heal bot. If you do play a healer to be a pure healbot and have full epiced out gear please link your toon because I highly doubt that many such players will exist.
Long story short - encourage more divines, even if it means they will be slightly OP.
I think if we want to make the game harder, make it harder in a way that doesn't make it disproportionately harder on the healers.