If you are running a commmodity product like MySQL with the AWS hosted offering, then AWS is effectively replacing the network, server hardware and server OS layers that your organization would have to acquire and manage some other way. It is definitely true that it requires a different set of (non-trivial) knowledge, but the time and cost of acquiring them is significantly lower than for learning equivalent on-premises infrastructure. The MySQL knowledge is more of a fixed constant, since you need that regardless of how you host the databases.
It is definitely true that if you invest AWS/Azure/GCP, then you still need some Ops-orientated people, and many developers don't have much interest in it. There is an issue of Dev and Ops being different mindsets.