Your argument seems reasonable but consider the fact that the technology of devices is improving over time. Mining devices are more powerful, consume less electricity. Renewable energy will also play a big part in the evolution of miners' equipment. One thing I am sure of is that mining will stop if miners lose money so they will always find a way to fix it.
At present the miners have the opportunity to mine 144 blocks on a daily basis which is basically 900BTC which is around $43.3 million dollars and these big miners will be willing to update their mining rigs if they think it is outdated and it has become a competitive space and that is what it should be, it is a capitalist market where anyone spending more money will reap more 
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