If you want MCH to be support, let us be support.

[ArtificialxSky]

Until it's on farm and MCH/BRD are back to being "the classes that do less dps".

This is never the case. Even on farm--even in speed runs, especially in speed runs-- their regen abilities are invaluable. In FCOB, SMN, healers, melee, WARs and PLDs were all running out of resources while farming.

Now, I want to address your main post, and allow me to rant at length:

In support of your first point, I'd say that removing the damage penalty, considering TP/MP regen already has a cost--the caster's MP--, is a very fair rebalance.

As for the other suggestions, I believe they would push MCH into the realm of being hilariously broken. A perpetual 5%, even 1%, general vulnerability up, or general decrease in damage received, is, in fact, an exorbitant amount of amplification/mitigation over the course of a 7-10 minute fight, and would make MCH already more in demand than it currently is for raiding. And it is in demand, ever as much as BRD.

Now, as for how this suite of utilities looks for MCH--vulnerability increases and damage mitigations-- let's look at a tried and true job that has performed some of these tasks admirably all throughout 2.0 and has become a teammate without which I hesitate to go into raid content, in progression or on farm, or on speed runs--the BRD. No damage mitigation, fair enough, we'll skip it. But Foe's Requiem: it's true that BRD has a long lasting Foe's Requiem, which costs MP, but unlike the other songs, does not decrease the BRD's own damage output, and increases an enemy's vulnerability to magic damage by 10%, for as long as 50 seconds! 50 seconds. The catch is that it is a song and so can't be used in conjunction with Army's Paeon for TP or Mage's Ballad for MP. No big deal. Foe's requiem is amazing for your mage's opener.

Now, my static has two mages. Even if we had only one mage, BRD's utility is set, but we have two. BRD just became MVP of eternity. So. My static has a BRD for Alex Savage ready to go next Tuesday. We also have a TP starved DRK, PLD, and me on melee. We need her with us. I need her with us. No doubts, no holding us back, no nothing, just solid, nay, necessary support. Okay? BRD has a place. I'll repeat, it is valuable and is holding no one back. It is holding no one back.

From this example, one can argue MCH, of a very similar cut from BRD, also has just as solid, nay, necessary, a place, just as BRDs do, in a static. Whereas MCH's Hypercharge vulnerability increase only lasts a "measly" 10 seconds compared to BRD's 50 seconds, consider, for a moment, that MCH's damage amplification is variable between either physical vulnerability (hello double melee comps and BOTH tanks that have always been there!) or magical vulnerability whenever you might need it, all at the user's whim, and can be used while switching out Promotion on the turret, and doesn't cost MP to use. In other words, IT'S FREE!!! (On a side note, even in a double caster composition like my own, Rook Turret Hypercharge would be more valuable raidwide than Bishop's since physical damage still outweighs magical damage in the raid, meaning MCH's ability might actually amplify a greater amount of damage, overall, than BRD's Foe's; and especially so in a double melee comp.)

Now to show how similar in value you, MCH, are, like the BRD, understand that in FCOB, a BRD might get to play Foe's Requiem exactly once in the entire fight, and will, I might reckon, exactly once in these upcoming Alexander Savage fights. The rest of the time, the BRD is playing Army's Paeon for my TP (our tanks included of course) or Mage's Ballad for our SMN and healers. The MCH, on the other hand, gets to use Hypercharge whenever it is off cooldown, and then switch right on back to Promotion for our resources. Now, knowing all these trade-offs and similarities and the value of BRD and MCH's near-equivalence to this most distinguished of job-roles, will you, OP, tell me why, exactly, upon reflection, you feel as though you're "holding your group back"? Oh and I completely forgot to mention MCH has free damage mitigation! Hahahahahahahahahahahahaha! What?

I will say again though, removing the damage penalty while activating TP/MP regen is a great idea. ^^d