I don't know about that. Giving -PDT with Protect sounds more like something RDM (or maybe even SCH) should be have. I wouldn't be against WHMs being able to do the same thing along side RDMs and SCHs. But it seems strange to me that only WHMs would get a boost like that.
IDK, it only made sense to me because Shellra merits does the same thing with MDT. WHMs are capable of a notably stronger Shell effect than the other jobs.
WHMs can also get a stronger Protect, except this time the difference is completely unnoticeable and is never worth the extra merits.
I agree that it makes sense from a purely WHM Group 2 Merit perspective. But most jobs have crappy Group 2 Merit options. I would rather keep this merit option relatively crappy rather than increasing the gap between WHM and the other healer/support mages.
White Mages are the only job capable of casting Protectra. Scholar's can fake it using Accession, but it does not cast like Protectra (Uses single-target animation only) and it uses a strategem charge each time. Thus WHM is the only job which can obtain the entire line of Protect and Shell spells. This makes sense because it is traditionally a healers job to not only restore HP but to reduce damage in the first place.
I'm not entirely sure why you think Protect is a RDM's domain. They might get higher enhancing magic, but that's only because they boast many different magic spells to enhance their own personal ability in combat. They actually have relatively few spells which are cast upon a target. The most notable ones are Refresh and Phalanx II, the latter you only get via merits.
RDM is a largely a very selfish job (The class, people, not the player). The bulk of its enhancing spells are self-target only. They're the only job to get single target barspells and gain spells. Somehow this doesn't shout to me as being a likely candidate for a spell designed to benefit the team as a whole.
FFXI: Seiowan Lvl 99 WHM, SCH, BLM