Recent 24 watt diode laser engraver seems to be putting out 14.5 watts on materials test

Yes a ramp test is the correct way to find the real focus for a laser. This guy explains it better than I can but be warned he waffles on a lot. oops wrong on this is the one but both are a good watch.

All other variables being the same, yes. But no, all other variables are not the same. You are making no allowance for the dot size of the beam. If you spread 20w out over a larger area than 10w, you will obtain an apparent reduction (loss) of power.

No need to tell us you are a Professor. I am not, but I am a member of Mensa. Does either of these change the laws of physics?

Laser bad, replace it. Is knowing why really that important?