I haven't found this to be true generally unless your workloads are truly completely static, which I've never actually experienced.

Given what engineers at this level cost, their costs per hour dealing with all of the nonsense clouds handle for you (networking, storage, elastic scaling, instant replacement of faulty servers, load balancing, yadda yadda) end up being higher than whatever tax you're paying for using the cloud.

Economies of scale are real.