So I'm finally getting down to doing this thread, of which I did say I would do in another post.
First thing is to explain my position on this class, keep in mind in no way am I trying to defend some of the problem this class has, this class is a Debuffer not a Supporter. In no way does Debuffer mean DoT DPSer, as some individuals who shall not be named believe it does, infact the difference between a Debuffer and a Supporter is all about how they go about it. While a Supporter will directly buff the party in some way, like a BRD's songs, a Debuffer will instead lowers the enemy stats. It is important to note the difference as it will some what effect how the class interacts with the rest of the party.
Now one of the biggest things I hear as an argument to that MCH doesn't bring any kind of unique debuff to the table that other classes don't already have. This is both right and wrong. Let's do a solid breakdown of the skills MCH and compare it to the skills other classes have that it would match up with.
Lead Shot: It's a Dot, see well any other dot.
Leg Graze: Heavy +40% Duration: 12sec
Similar effect from Acn, Ast, Whm, and blm: The biggest difference between them is that MCH is oGCD like Acn but has a much shorter recast time.
Blank: 15-yalm Knockback.
Ok yea the only two I can think of that have this are Whm, and Carbuncle, and yea it shouldn't really be used to often unless something goes horribly bad or the enemy can't be knocked back anyway. (Not even really sure I'd count it as a debuff, but hey it does interrupt when used so meh)
Foot Graze: Binds Target Duration: 12s
Ok so yes this effect is shared with Brd, Smn, and Blm. However it lasts longer than Brd and Blm, and is another oGCD ability.
Head Graze: Silences Target Duration: 2s
Yea shared with Brd, Pld, Mnk, and Nin (so long as nin isn't using wasp venom) not much else to say other than another option to interrupt a spell here.
Suppresive Fire: Stun Duration: 2s
Yea I'm not gonna bother naming everything that has a stun here, let's be honest this is pretty much a staple move for all classes at this point.
Now for the big juicy bits that really make this class. And by big and juicy, I mean tiny bits that really should have been better but are what kinda set the class apart, or attempt to at least.
Dismantle: Lowers the targets physical damage dealt by 5% Duration: 10sec
This ability(along with Rend Mind) are often compared to Virus, and yea I see it. However, I'll make the counter that while Virus effects the stats, this directly effects the damage being dealt, which takes into account other variables.
Rend Mind: Lowers the targets magical damage dealt by 5% Duration: 10sec
See above
Hypercharge Rook Turret: Potency: 160 Increases targets physical damage taken by 5% Duration 10s
Yea I'll agree this is a weaker version of Nin's trick attack, except that it also allows your turret, which attacks separately from you to hit harder.
Hypercharge Bishop Turret: Potency: 120 aoe Increases targets magic damage taken by 5% Duration 10s
....See above
Ok now onto "those" support moves someone is bound to throw up as some sort of argument for this class.
Promotion: Turret stops attacking (grouse), Rook regens TP, Bishop regens MP, both in a weak amount with a 20-yalm radius around the turret, Hypercharge doubles the regen.
Yea Brd in fact does this better. With the stationary-ness of the turrets this is really just an as needed ability for when your group is really hurting, probably late fight if even that. Though, maybe early in the fight so for the initial pull your nin doesn't have to waste his goad right off the bat.
Ok so having gone through all that lets talk about what MCH brings to the table here shall we. Yes, all of this is, in one form or another, covered by other classes, but it's not covered by all of the classes individually. Think of it as a kind of Merged class between Brd, Acn, and Nin for these debuffs. Also all of the important ones stack with the debuffs of all the other classes.
So now for the important, what's actually wrong with this class section..... MCH is one massive pain to get any sort of payoff at all. That being said, there are ways to fix it that would be fairly simple, to fix it's payoff and make it more wanted in a party, I'd recommend increasing the effects of those debuffs, and maybe the durations too though not by much. To fix the dps issue, well increase the Proc chance on the 1-2-3 doesn't have to be by alot, and decrease the recast time on Reload and Quick Reload, that should do it there.
Final thoughts: Well clearly I was wrong about the rapid fire thing, which now makes me sad.
Clearly this class is not meant to work alone, and, to me, seems to have a heavy focus playing off what the rest of the group is trying to do as you can get some pretty big % based minuses onto the enemy when everyone is doing it all at once. However, while this might have been the idea the devs were going for, it's ultimately a one off big numbers chance and when it's done the MCH is kinda left sitting around for 90sec doing, honestly, pitiful damage.
Edit: As discussions go on I will update this and add info and possible ideas of ways to better use this class.