Both attitude and power determine descent angle and speed. There's no one-to-one relationship: like many things in flying there are many parameters.
The 'gearing' between the outputs (descent angle and speed) and the inputs (attitude and power) depend on the shape of the drag curve. If you're up at maximum cruise speed, putting the nose down a little will not change the speed much, but it will produce a significant descent. At best lift/drag speed, the same change in attitude will alter your speed, but it won't put the aircraft into much of a descent.
So whether you use attitude or power for glideslope control depends on your aircraft and the part of the flight envelope you're operating in. I suspect the difference you perceive between light aircraft and military/commerical transport aircraft is a consequence of the different types and envelopes.