> The optionality of being cloud agnostic comes with a huge cost, both because of all the pieces you have to build+operate

This sounds like cloud vendor kool aid to me. Nearly every cloud vendor product above the infrastructure layer is a version of something that exists already in the world. When you outsource management of that to your cloud vendor you might lose 50% of the need to operationally manage that product but about 50% of it is irreducible. You still need internal competence in understanding that infrastructure and one way or another you're going to develop it over time. But if its your cloud vendor's proprietary stack then you are investing all your internal learning into non-transferrable skills instead of ones that can be generalised.