My impression has long been that the endowment per capita metric provides about as good a ranking as any of the third-party rankings within a category. Where it disagrees with US News, it usually matches my intuitions; and where it disagrees with my intuitions, I usually learn that the college in question has a better reputation than my impression.
It doesn't do a great job comparing across categories, but then, neither does US News...
They still do great on this metric, though! MIT comes out looking a bit short of Harvard, on par with Stanford. These schools ride a bit higher than the top tier of LACs (Williams/Amherst/Pomona/Swarthmore), which isn't necessarily the fairest comparison, but Caltech fits right in with those.
Maybe they'd be richer if their admissions was more open about taking quasi-bribes, but I suspect you're dramatically underestimating the orders of magnitude of difference that appear on this metric. You find clear tier gaps.
Don't get me wrong, this is a silly proxy metric about three degrees out from anything you'd actually want to know. But it gets surprisingly good results for how simple it is to tabulate.
It doesn't do a great job comparing across categories, but then, neither does US News...