Somewhat isolated, yes. Not protected because there are no privileged instructions on a Z80. Bank switching requires part of the address space to be common amo

Somewhat isolated, yes. Not protected because there are no privileged instructions on a Z80. Bank switching requires part of the address space to be common amongst all banks (never switchable) so code to manage the switching can execute. In that part of the address space you can do things like monkey patch the OS and driver entry points, or switch banks and collect or patch all the RAM.