There is one more argument one might make why ROM shouldn't be considered firmware:
It's possible to have two functionally equivalent chips, one hard-wired to do its job, and the other with an embedded MCU and firmware ROM.
And they would be externally indistinguishable.
Therefore, if one demands that ROM firmware be free, one should also demand that hardware be free.
Which I think is also a valid maximalist stance, and I'd be happy if FSF was to take it.