That’s definitely the right call in some cases. But as soon as there’s any high-interconnect-rate system that has to be in cloud (appliances with locked in cloud billing contracts, compute that does need to elastically scale and talks to your DB’s pizza box, edge/CDN/cache services with lots of fallthrough to sources of truth on-prem), the cloud bandwidth costs start to kill you.
I’ve had success with this approach by keeping it to only the business process management stacks (CRMs, AD, and so on—examples just like the ones you listed). But as soon as there’s any need for bridging cloud/onprem for any data rate beyond “cronned sync” or “metadata only”, it starts to hurt a lot sooner than you’d expect, I’ve found.
Yep, 100%, but that's why identifying compatible workloads first is key. A lot of orgs skip right to the savings pitch, ignorant of how their applications communicate with one another - and you hit the nail on the head that applications doing even some processing in a cloud provider will murder you on egress fees by trying to hybrid your app across them.
Folks wanting one or the other miss savings had by effectively leveraging both.