My first sub 30min AK run was a double DRG party. BLMs are consistently the worst dps I encounter (not worst as in they do always bad dps, worst as in most consistently lower than other players - the good ones are very damaging).
Don't pay attention to what other people are shouting in MD. It has no bearing on you. Form your own party.
The only time it's a problem is if public perception of certain content/classes makes it very difficult to form your own party, but the only case I've ever run into that was HM Titan as a War (and when I did clear it, I cleared it tanking with two SCH healing, hardly optimal).
For speedrun stuff, they're asking for certain gear/people because they want to clear boring grindy content in the fastest possible manner (even if, on occasion, they don't even understand who/why/what they're taking, they're just aping what they see other people doing).
If you want to do it normally, form a party for just that - don't just shout in MD, go FC->LS->Friends->Shout, and shout in each major area (MD, Coerthas, CdS, QM, and each city). You will get a party together doing that unless it's a really odd hour of the day or something.
If you have an irrational dislike of people shouting for speedrun parties, wait till you have every piece of possible gear from AK and it's the only place you can get Myth tomes from and you'll understand why they're doing that.
It's also worth mentioning that if you have no intention of doing Coil any time soon, you shouldn't even care about Myth, since there will be more sources of it shortly, and Crystal Tower will have ilvl 80 gear soon.
CM/Praet speedruns are equal parts gearing up in Darklight and gearing up in crafted and selling crafted mats for good gil.