> I’m now beginning to question if it’s closer to a weird vitamin that we face a systemic deficit of.

There's some studies suggesting that a big part of what influences someone to naturally be fat or skinny is tied to natural production of the GLP-1 hormone. Post-prandial readings of serum level GLP-1 show significant differences in lean people vs. obese people, with obese people have much less.

We don't have an understood mechanism yet to determine if it's causative - maybe it's yet another feedback loop we have with gaining weight - but it seems very plausible that the natural level of production is a determinant factor in just how susceptible you are to packing on the pounds in today's food-rich world.