Enfeebles cannot possibly be a reason to sub rdm as they are not rdm exclusive, with the exception of gravity. So it does come down to convert and fast cast.
Everytime I use /WHM I feel crippled in damage because I don't have any native MAB job trait. I use /WHM exclusively for situations where I have to cover Staff and Club Ws (which is stupid design imo, but a different topic) and I have no real reason to use /BLM as I feel that fast cast and convert have much more impact.

My Jobs are SCH, SMN and BLM and I only consider the first two of them my mains. With the lack of a more potent cure I just cannot always keep up with the damage dealt. Accession + Stoneskin is not as strong as it used to be back in the 75 days.
With a raptured Cure IV + aurorastorm + obi + cape and a cure potency atma I can break 800+ HP healed but it is still restricted by the number of charges available.
An overhauled version of Cure V (kill the low enmity cap for not WHMs, as it has been suggested a million times), we could at least alternate between cures.

As of for addendum:black I hope that once we learned all t5 nukes, they lift the need for addendum:black for t4 nukes.