That’s the thing, if you meet a (very low) bar of skill then bringing a healer IS an active detriment because they do less damage for functionally no positive gain outside of being a safety net the party really doesn’t need. This also allows you to skip mechanics and generally make the run faster
A healer is only not a detriment when the safety net is needed. But you can argue the same “tanks are needed” when the SMN was either really bad or the party was bad at managing agro. They are both just a facet of meeting the low skill bar needed to perform the off clear