I understand completely what you are saying and I'm just pointing out that this statement is false:
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If it mines less bitcoins than you have paid for it (or that you could have bought when you paid for the machine), then you did bad.
It's not bad, it's just worse. There is a difference
I don't think you understand that many people paid in BTC...not fiat. Many people DO NOT cash out to fiat (or buy BTC). If you don't make back the BTC you spent, you've lost something....that is a bad investment.