It is not flawed. The subject is under study, continually. The debunking comes from https://www.pnas.org/content/118/4/e2016976118 https://www.pnas.org/content/

It is not flawed. The subject is under study, continually. The debunking comes from https://www.pnas.org/content/118/4/e2016976118 https://www.pnas.org/content/118/4/e2016976118 where yes, many measures of happiness seem to increase linearly as log(income) increases. That means diminishing marginal utility of money, but it does not mean there's a cap - the relationship seems to continue at all income levels. The main reason to believe the famous previous research was in good faith and could still miss this result is because the previous research used a measure of happiness which itself capped out, and so _could not detect_ changes in happiness after a certain level. If your instruments can't register any changes above some amount, it is no wonder your results level off and stop at that amount. This new research could be wrong, of course. But there's no mis-summary here.