i feel like we're not even playing the same game.
MRD WSs are hitting for 100ish or more each. GLDs are doing like 15-20. the aggro generated from abilities is static. enmity is not reduced from taking damage. GLD block is useless after a point and they don't really have anything more than MRDs to mitigate magic damage.
so they have generally the same *abilities* for generating enmity, but MRD is outdamaging GLD by a significant multiplier.
considering GLD block abilities are pretty useless for this fight, there's no real point in bringing them over a mrd. you're generating a lot less top-end enmity so you can take maybe 4k less damage over the course of a 10+ min fight... and 10+mins is awful. if you're doing it in 5mins, it's quite a bit less than 4k damage. and either way your cnj (or cnjs? lol) should easily be able to handle it.
i've grouped with maybe one amazing GLD that was able to do 13+ dps on ifrit, but generally most GLDs are only going to be doing 7-9ish. MRD can very easily push 15+ dps, and should be capable of 20 if they're in an all-THM group (thereby not really needing to worry about MPKing lancers by turning ifrit around)
yes GLD works, and it works fine- but that's not the point. the point is you'll have less enmity issues (on ifrit) with a good MRD tank.