You have to skimp on your duties far too much to off-set that number. Meanwhile unlike a RDM hybrid, a BRD front-liner is adding upwards of 20% to each melee including themselves with buffs. The back-line WHM(healer) should already have Dia and haste covered on melee so you tell me which support helps more?
I have to love the arbartrary refrences like "too much" and "duties". Situational **** is situational.
For instance. You compare WHM Dia to that of a RDM's, you're already down 5% between tier II and tier III, assuming that WHM even uses Dia at all, which is most likely no the case (sorry but we live in a world of facts, not 'should's). Then you have the issue between the limits of a BRDs buffs and RDM's debuffs. It's nice to claim that BRD provides a nice 20% damage boost, which is true if all you're running is a single party full of jobs that are pure bread and butter DDs. Tack in any pet jobs or any jobs that use other sources of damage besides straight melee, and you loose that advantage instantly.
Defence Down, however, is universal, more universal than haste, in and of the fact that it affects every physical damage calculation from Melee to WS to Ranged to Pet Damage to Blue Spells. It also spans further than 'party wide' such as bards go. So the larger your group, the more important the defence reduction is. Again, best refrence here is "Angon on every mob, that STACKS with Angon." For the frontline rdm/dnc. This is on top of the future haste samba and drain samba and aspir samba depending on your situation.
Depending on your situation, sure BRD can do a whole lot with it's situation (More than RDM with more ease so long as he's placed correctly.) But then again, they also sacrafice something in that situation. BRD's complications with melee are similar to RDMs in the fact that BRDs who are not toting around a Relic will suffer potency/druation issues to keep from having to constantly swap their instraments to prevent TP wipe. However, instead of it being a mear Macc issue (like with elemental staves.) It really does have a pretty sizable effect on BRD's support aspects.
In the end, say if you had both a BRD and a RDM that wanted to take the front lines for a Dynamis run, put the BRD in the heavy DD party and RDM in the tank party with a WHM (Or SCH) and you'd be set.
There's another matter here we need to bring up.
With the shift in endgame, especially concerning the relative ease of endgame thus far, I beleive players in general are taking themselves and people around them far too seriously.
Granted, a lot of some of the things in game (like magian trials) still do take a bit of work and effort to get accomplished. But most of it is simply time sinks. "Hard Fights" are usually reserved to the HNM level that most Red Mages are completely fine back-lining for.
Abyssea EXP parties themselves allow for level 30 leeches to sit and do nothing but pop chests while virtually anyone could do key management without as much loss to party performance.
City Dynamis is so laughable now that laymen groups are clearning the zone completely out with time to spare.
So really what is the conflict here. "Time effiency?" "You could do better on X job with Y combination?" Please. These are semantics arguments at best barely even factoring in to the game proper when gimp DDs and half *** mages are far more commonplace than any anti-melee camper can bare to admit.
Yet people are crying wolf over the tiniest things like not maintaining an absolute perfect haste cycle or not pulling as much damages as a dedicated DD. To that I ask, so what?
"I Could have spent that 10 minutes doing attempts on my AF3 quest" is total and utter ********* If you're in Dynamis, you're doing dynamis, you're not like "omg I gotta get dynamis done so I can run to abyssea to turn in my galkan sausages!" If you're that pent up to do that, you've either already done it before dynamis prep time or you're so obsessed that you're going to do it after regardless of how long Dynamis took.
People really need to lighten up and get a grip on reality. In 90% of the situations a RDM would even bother arguing front lining, it's not even an issue if they do or not. It's not 2005 anymore.