You could argue that using RDS means they face less devops work than if they ran MySQL on their own dedicated servers. That might true in some aspects, but then, with RDS, you also need to keep track of some issues that are specific to AWS. Availability zones, regions, management via console versus the AWS CLI, management of the keys, etc. So there is the question, which you must ask yourself, and your team, do you want to be learning skills specific to the technologies you are using, or do you want to be learning skills that are specific to AWS? Would you like to deepen your knowledge about MySQL, or would you like to instead spend time memorizing the various decisions that Amazon has made?
I'm not suggesting that there is a right answer, but I am suggesting that the answer is much more muddy and nuanced that Amazon's marketing suggests.
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.