OOOH, having just seen this I have some midnight musings-
Super interesting but I feel like this reads into it a bit, especially because Martin doesn't benefit at all from the buried treasure, just Carolyn and Arthur (who it's implied earn it by surviving having Gordon as a husband/father respectively) and Douglas (who doesn't earn or deserve anything, he just gets stuff by being charming and wily). Martin specifically doesn't financially benefit from the gold AT ALL- he benefits from finally getting his shit together and getting a real big kid job.
I also don't think any of them ever claim to be economically poor except Martin, who as you note is the architect of his own misery and by the end of the show has managed to get a grip. (I also think the emphasis on him being POOR, rather than just un/underemployed and kind of sad and pathetic, comes largely from Qik- an episode I Do Not Like, as it happens- and the ensuing fanon; it rarely comes up through the lens of poverty per se as opposed to Martin's frustrations with not being paid for his work.) I'd note as well that it's stated that Martin's mother is extremely supportive of him and of his dignity, is financially doing fine, and likely would help him if he asked for it. Not that it's not possible to be poor coming from a middle-class background, but Martin is clearly not in that situation due to anything other than his own choices and I don't think the show ever pretends otherwise.
I don't even think that Carolyn ever claims to be personally worried about money on the face of it- we know she has a big house and a nice car, and that she's pouring all her money into MJN for the same reason that Martin is working for her for free, though she'd never in a million years be okay with that comparison. And similarly for Douglas- he isn't the kind of person who talks about what he loves, but he clearly loves being a sky god, and despite being the kind of guy who I'm sure could talk his way into a better job on terra firma, he's not going to jeopardize being the sky god (and as we learn from Zurich it's not even about flying, it's about being AWESOME while flying). All of which is noted here, obviously, but again, I don't even think the show is making a case for them being poor, just, MAYBE, poor relative to their customers, which makes sense because they're the kinds of people who can charter private jets.
We sympathize with the MJN crew when they worry about money because we care (like them) about the wellbeing of MJN, not their personal financial statuses. We get the feeling that they'll be fine, which is why the start of Zurich, when it looks like MJN is folding, we're sad about MJN and worry about Carolyn, Douglas, and Arthur's fulfillment but we don't worry at all about them financially. We never once think "how will Carolyn buy groceries" or even "how will Douglas make his alimony payments" (which reminds me, can't remember, does he canonically have those or is that a pure fanon thing?). It's all about the personal things that MJN brought them and nothing more. It's actually almost a good thing that JF deliberately doesn't emphasize personal financial instability as a factor or things would be much more anxiety-inducing!
Of course MJN are underdogs, but they're not positioned ever as the proletariat or whatever, and their underdog position is not implied at all to be because of financial disadvantage per se. It's because they love flying/MJN/being a sky god and because, as noted, they're at least a bit crazy.
