Heat and hotness don't mean the same thing in this context [1]. It doesn't help that the article seems to use heat (energy) and heat (temperature) interchangeably, but the principles of backside power delivery exacerbating hot spots and increasing peak temperatures will apply regardless of wattage or efficiency. A hypothetical (poorly designed) future M-series chip with bspdn could actually emit less heat specifically because the hotspots get hotter faster and cause throttling sooner.