it breaks the fundamental freedoms that make up “FOSS”
Why? All the license says is that if you provide it as a service you must release the source code.
It says that you must release all your source code, even the stuff that isn’t covered by the license. From Wikipedia:
anyone who offers the functionality of SSPL-licensed software to third-parties as a service must release the entirety of their source code, including all software, APIs, and other software that would be required for a user to run an instance of the service themselves,