I guess that in this very specific environment, the only practical reason against the Pis are the containers. Spotty support for ARM images seems to be a continued problem.
I didn't know that was a problem. I run all my services in containers (only service on the host is ssh) but it's all from Debian repositories and so would run on basically any architecture. I guess it depends on how specialized the software is that you require but what is built into Debian is quite extensive in my experience.