Not necessary
> or filesystem access
Also no
> or ability to modify the fleet.
Not that either. It feel like the conversation around these things is stuck in the far past. Large-scale organizations can and have driven the number of people with root passwords to zero. "Filesystem access" shouldn't be as easy as you're implying and it also shouldn't be of any use, since everything in the files ought to be separately encrypted with keys that can only be unwrapped by authorized systems.
Even the last thing you said about Linux systems starting processes ... even a minor application of imagination can lead you to think of an init daemon that can enforce the pedigree of every process on the machine.