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>earning a lot of ETH for a fraction of the previous cost

That will only be true if mining is a significant contributor to the availability of ETH. Instead, I think that most ETH comes from sellers of existing tokens rather than miners.

The rewards are decreasing as well. Issuance is reduced by 90% from currently ~13k ETH/Day to 1600 ETH /Day.

How do you know it's a "fraction of the previous costs?" You do need to buy ETH instead of hardware. I did some quick searches and got varying interest rates, so I'm not sure what the expected return is.