I know, that's why I said holding everything else constant.
Yes I see that now. But realize that in real life, it's impossible to have everything else constant when it comes to bullet weight. If a heavier bullet and lighter one are pushed at the same speed, speed may be constant but power factor is not.
If a 147 gr bullet was shot with the same speed as some +P 115 gr commercial rounds, to 1350 fps for example, the 147 gr bullet would have a power factor of nearly 200. Minor PF is only 125 and major PF is 165. Most people shooting 9mm major shoot open race guns that are specially designed to handle the high pressures caused by such rounds. But 200 PF? I'd be waiting safely on the other side of the berm while you tested your first round.
Whether commercial rounds or home made according to directions in a reloading manual, generally the heavier the bullet, the less power is required, and the less velocity is achieved. But chamber pressure and power factor remain fairly constant across loads appearing in the same min-max scale.
Everything is relative I guess