There are three methods that have been mentioned so far - farming shards, farming the Matamata in the field, and farming a fracture (with an option for the Matamata there as well). I've only flatly dismissed one of those as non-viable - farming shards. I believe I've offered a solid reason why the second option - farming the Mata on the field - isn't viable (limited spawn).
This leaves only one method with any merit (not "several"): farming a fracture. But are you then trying to convince me that one method - that by all given suggestions requires an high-end PLD or someone willing to zombie in order to actually be viable - is something I should just quietly accept? That is not likely to happen.
Am I wanting "99% as much plasm as 18-man groups"? No, of course not. A decent 18 man pickup-up plasm farm can earn around 5,000 to 6,000 plasm. I don't think it's too much to ask that 6 people then be able to earn, say, around 2,000 across that same time frame. One-third the people, one-third the plasm. Zagen did mention that amount earned, but again, fracture farming with a PLD/Zombie is the one and only method I've seen suggested that has merit, and this thread is about trying to get more than one option.
(To forestall the inevitable: Farming the Mata in the field, yes, can earn around that much, with a bonus mix of airlixirs, to boot. But, again, that one NM in the field is not a viable option due to the limited access.)
Lastly, to address your comment about "easy mode": Asking a nearly unkillable PLD (or entirely killable zombie) to babysit all the big nasty NMs while everyone else slaughters mooks is about as easy mode as is gets. It is not at all challenging, merely tedious. Yet another reason to want more than one viable option to earn plasm on a reasonable scale.
Ah, you know? This was a total brain-fart on my part and I take back what I said about it being extremely limited. I had the twilight stuff confused with the gear from Fiat Lux. My apologies.