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I didn't realize you were so specifically referring to obsolete Bitcoin mining equipment. Regardless, I still contend that electricity, if it is to be utilized in heating, is more efficiently made to produce heat with equipment designed specifically for the task.
Not true. Electric heating basically dissipates heat in a resistor and then in many cases has fans to distribute the heat. This is no different from electronic equipment, only that the resistor is replaced by the various integrated circuits. In both cases if one puts in
500 watts of electricity in one gets 500 watts of heat out. This is just the first law of thermodynamics.
https://en.wikipedia.org/wiki/First_law_of_thermodynamics.
Your statement does not account for electricity lost to other forms of energy.