This hasn't been my experience. Replace sysadmin with cloud engineer/architect, salary bump, no reduction in quantity. This assumes you are mildly competent as an organization.

On managed services, say the database. My experience is that the extra costs of the service are larger (usually much much larger) than any salaries or head count reduction. I'd rather employ more people than not, and actually control my data, given the choice. Particularly when the savings are questionable or false.

I generally prefer a lower dependency count. Code and vendor. Even at modest immediate cost increases, you gain better flexibility and there are less things to bite you.

> Reduced costs in off peak hours with on-demand instances.

Agreed. You do increase system complexity to accomplish it. But there are actual cost savings here.

> Right sizing resources to application needs.

This isn't unique to cloud, you can do this in any hypervisor. This is a basic feature.

> There are wins that one can have, but nothing is guaranteed

It does not "always" hold. This is critical missing nuance in the original claim.