The tech tree APC squad allows for 5 rifleman + 1 Driver, and a mix of other specialist roles, but the premium APC squads only allow for (a higher amount of) specialist roles, and no riflemen.
I’m not sure if its an oversight, or a design decision, but my suggestion would be:
Give premium APC squads 5 rifleman slots.
This would allow the use of a more simple squad composition when you just feel like driving up to an objective and then pulling out your bolt-action rifle of choice, or whatever else it might be.