You gain already about 100% by switching from air-water to water-water. Then on top you get the heat pump to extract the heat from the water more efficiently by preheating it with the miner. Finally, you can use the cooled water to cool the miner, increasing the efficiency of the miner and reducing the power needed to cool it.
Discussion
The first law of thermodynamics wouldn’t even allow to reach 100%.
These high numbers are only valid, because the heat pump isn’t a closed system and it purposely draws in energy from the outside.
Go talk to a physicist about your last two notes. I'm sure he will have a good laugh, and you will learn a lot. Win-win.
Or maybe you should 🤷
Explain to me the limits. Why do you say that a heat pump can only get 400%, not 500%?
And then explain why there is groundwater based heat pumps that go up to 500% that you can buy right now.
https://www.heizungsfinder.de/waermepumpe/wirtschaftlichkeit/wirkungsgrad
I won't fall into Brandolini's trap.