Comment by zmmmmm
It has other advantages.
Operationally, it is very nice to be able to update one discrete function on its own in a patch cycle. You can try to persuade yourself you will pull it off with a modular monolith but the physical isolation of separate services provides guarantees that no amount of testing / review / good intentions can.
However, it's equally an argument for SOA as it is for microservices.
There are some other benefits like having different release cycles for core infrastructure that must never go down vs a service that greatly benefits from a fast pace of iteration.
Literally one function per service though is certainly overkill though unless you're pretty small and trying to avoid managing any servers for your application.