I think the anecdote highlights that there's no incremental way to approach gRPC, it's not a low risk small footprint prototype project that can be introduced slowly and integrated with existing systems and environments. Which, well, it is a bit of a fault of gRPC.
I think that's not true. There are plenty of incremental ways to adopt gRPC. For example, there are packages that can facade/match your existing REST APIs[1][2].