then “employer contributions to health-insurance premiums” have become pretty-much the largest overhead-cost of having you on the payroll

The amount I pay out-of-pocket for my employer group health coverage and the amounts I've heard (I've not checked myself) for similar plans on the exchanges implies my employer contributes very little to my coverage. If my health coverage is the largest part of my "fully loaded" cost to them, then they're being screwed by somebody in their HCM supply chain, not by health coverage costs.