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.

[1] https://en.wikipedia.org/wiki/Heat#Heat_vs._temperature

good for a laptop. what would the clocks be on a desktop part that was liquid cooled?

I have an M4 Max MacBook Pro and it generates plenty of heat, especially when gaming, compiling, or transcoding. I think that's still far less heat than it could've generated if it weren't Apple Silicon, though.

Are you dismissing a technical article with detailed explanations and arguments about the future of CPUs by simply mentioning some piece of current consumer hardware?

The Apple Silicon chips are indeed running hotter on every new generation, no?