I understand you prefer whm and thats fine. But I really just think you've partied with some very shitty rdms. Yes I agree it is easier to heal with a whm especially with them having Cure V and higher level curagas. A rdm has to cast more spells to heal the same hp.
One more level of clear mind and conserve mp pales in comparison to Convert, which effectively doubles my mp pool, and Refresh and Ill take the pepsi challenge anyday of the week that'll I'll keep up if not surpass a whm healer pound for pound if we have to heal the same amount of hp over the same duration.
What I notice is most whms just heal and haste and do very little else. Rdms, even though we're healers of the cannon are always asked to do more things (ie tossing out refreshs, dispeling, enfeebling, etc) and it takes a toll on our mp pools. If all I did was pure whm duties such as heal and haste, I don't care what kinda cannon you got, a good rdm would keep up.
Like I said it just sounds like you've played with some really bad rdms and happen to know a very good whm and are under the wrong impression or have been mislead to believe we can't be effective healers in a cannon.
Effective healers yes, the best healers no. Convert does not make up for the faults found in RDMs. There is only ONE enfeeble ever asked for in a cannon, DIA II...and due to the nature of the spell, WHM suffices to land it just fine. Getting buffs to stay on the party is immensely difficult for a RDM unless you settle for PRO/SHELL II, which can lead to deaths in the party if you settle for this.
PRO/SHELL V without great mp loss + Regen III + Cure V + Conserve MP + Divine Veil (if needed) + higher Clear Mind
OR
Refresh + Convert + Cure IV as highest curing spell, which lends to problems if possibly mistimed.
If Melee are acting as they should, they'll land vokes in on incoming mobs if more then one voke is present to keep the BRD puller safe. Should that same melee have damage done to him and get cure IV'd after the voke occured, the RDM will have a great deal of initial hate. Then when the mob is woken by a melee hit, the mob goes for the RDM, and a voke may or may not stop it from getting one hit in, interupting resting and losing any HMP that may have been occuring, AND forcing the melee to have to manuever more, losing seconds off of the impending kill.
Situations like these add up. No matter how good the rdm is, times like these will occur ONLY due to the nature of the job and spells available. A couple seconds here and there is the difference between a solid chain 200 party for 20-22k/hour and an explosive cannon that rattles off 25k+. I've partied with the best of the best rdms and whms, its not the player, its the job. Xtereem was an insane cannon RDM that I partied with a ton on aura weapons due to the need for dispel. Even though he has all the gear and skill a rdm could possibly ask for, I'd still be weary to invite him to a ToAU cannon over a WHM.
Uzor himself said that WHM > RDM for cannons because its easier. When you see how quickly we move from mob to mob in our elite (yes i said it) cannons, you can see how any wasted time can add up to lost experience points.
When I say a RDM is struggling, I'm not saying they're shitty. I'm saying its tougher for them and it slows down the party slightly because of it.