The real problem here is that MMA pay is low and needs to go up on the whole.
But for Dustin Porier specifically? No it really doesn't. So while he is paid less than he should be, everyone pretty much agrees on that, he isn't really being paid less than he should be in relation to his peers. On a proportional level.
Porier made around 370k his last fight I want to say, top of my head. 150/150 to show and win + bonuses and shit. Okay 150/150 seems perfectly fine for what Porier is. He is not a champion and he is not a super marketable draw.
The UFC could cut Porier and go on without missing a beat. He's a good fighter but he's not an awesome fighter and he will never be LW champion imo. He's the 4th best LW in the division if McGregor is to be counted as well, yes he is. And beyond that ranking him above Ferguson is a bit speculative as well. Ferguson was considered better prior to the Gaethje loss, a much tougher fight (after two weight cuts) than Dan Hooker (a close war).
Porier is a top ~5 LW for sure, but he's not popular and not a draw. Good guy it seems, talented. But 300k at minimum every time you win...how is that something to complain about in context, in relation to your peers?