While spending per student is certainly linked to endowment, there are schools with less than $10B endowments where spending per student is greater than all in costs.
Bowdoin, for example, spends more per student than COA.
Here is a link that shows 6 of the 10 LAC NESCACs where per student spend > COA, and some of them have <$1B endowments. https://bowdoinorient.com/2019/04/12/how-does-bowdoin-spend-its-money/
Wrt the article that OP posted, it is important to look at the financial health of any school on your kid’s list. At some schools, the full pays do subsidize those receiving aid.
There’s a great blog called higher ed data stories. There is an illuminating analysis of average discount rate by school (one measure of financial health), posted on Mar 27, 2019. It uses 2016 data from IPEDs which is still the most recent data available.