"glideslope is pitch, not power"? Is this something peculiar to an Autopilot approach?"
PA28
Here we go again
Neither is right neither is wrong!!!
The less powerful the aircraft, the more draggy the aircraft, the less experienced the pilot, the more pitch for speed is important.
You have two engines on a SEP
The conventional one operated by the throttle and the potential energy one in the airframe operated by the column!
both are sources of energy so think energy management not that rubbish of pitch for speed or power for speed.
Not rubbish where a student is taught to pitch to keep away from stalling in a high drag low powered aircraft but not the whole picture or truth.
Pace