Disclaimer:
Yes, I play MCH mainly so I'm sure my bias has taken root in my post and suggestion. Feel free to curb my boomstick enthusiasm as needed and provide constructive criticism.
Context:
(Feel free to skip to The Point if you're well aware of how the rDPS dynamic works, or to read and correct me where needed)
MCH, BRD, and DNC have this dynamic where their individual damage is balanced with the buffs and utilities they provide.
DNC has a potent single target, consistent damage buff as well as various other utilities (sharing its crit/dhit buff with dance partner, group heal in a pinch, etc), but tends to be the lowest individual DPS to balance it out.
BRD has a less potent but group-wide, consistent damage/crit/dhit (rotating) buff as well as other utilities (cleanse, increased heals, another dhit increase, another dmg increase). It generally does more dmg than DNC to be the middle-point between MCH and DNC.
MCH has no consistent buffs and limited support utility in the form of Tactician (which its counterparts have in their forms as well -- as such I'm not going to mention it for the rest of the OP). It's also the highest individual DPS of the three, but is known as the 'selfish DPS' due to what it brings to the table, or lack thereof.
The Point:
MCH is by no means unplayable or weak, and endgame content can be cleared with the job. However due to its near-zero utility it's often overlooked for the other two and regarded as the worst of the bunch.
I feel that should change. I understand the rDPS dynamic SE has fleshed out, but MCH having no utility is drastic and what it gets in return is either undervalued or not worth it objectively. I believe MCH should get a debuff ability (i.e. Vuln) to both provide it more value. It doesn't need to be anything dramatic since it is still supposed to be the least utility in relation to BRD and DNC, but enough to offset the lack of said utilty.
How would I see it implemented? In a preexisting ability. I would, for instance, suggest inflicting Vulnerability Up on a single target when Hypercharge is used. That can lead to a fairly consistent uptime that also can synchronize with the utility of other classes (Arcane Circle, Divination, Embolden, etc) for a substantial impact.
Imo, it fits the 'selfish' DPS nature that MCH has been redesigned to be. MCH is less focused on helping party members do more, and more focused on doing more itself. Sure, it also is a boon for other party members, but only if they're attacking what the MCH wants to attack. Thankfully in most content where balancing is looked at, it's usually a single target/boss fight.
Whatever the specifics of the debuff, it would have to be substantial enough to justify even adding it at all, but not enough to disbalance the dynamic SE wants.
TL;DR
SE pls gib vuln/something to MCH so I stop getting mogged by BRD/DNC