Unit has to be something fixed .. like a meter doesn't change its length unless it is traveling at relativistic speed :-)
Discussion
Each new block represents the current marginal cost of power, while older blocks represent the aggregate cost to rewrite the chain through that block.
Either way, it’s all about power. Bitcoins value is necessarily supported by the cost of power.
Power plus compute .. if someone made a more efficient hash machine , power consumption may reduce ..
You're talking about efficiency; power drives everything.
You work in 2025, and you buy a vacation 40 years later. That's energy. Use whatever you want to measure things in the middle, but dollars are the worst option.
Bitcoin is what fixes the unit. That's the whole point.