If you replace a network hash for hash you end up with the same hashrate and 1/10 the ENTIRE NETWORK POWER CONSUMPTION.
Disregarding the normal fluctuation in value of coins being mined. I don't see how this conclusion is arrived at.
Nobody interested in these devices is planning on continuing along at the same hash rate they are now with a GPU rig or farm. They will want and need more to keep up. Nobody is going to buy one and go "OK, I got the same hash as my 15 1080ti at 10% of the electricity so now I'm good this is it." Once they re-equip en masse then network hash skyrockets. Just like it does with an ASIC machine. They hit the network and difficulty goes through the roof. People then are under pressure to buy more to keep up. And so on.
Perhaps this is a better way to illustrate:
I have one gpu. I hash 1000 h/s @ 1000w.
I buy one FPGA. I hash 10000 h/s @ 100w.
Am I going to buy just one FPGA then? No. I'm going to buy 10 of the things so I can run 100x the hash at the same power. Just like everyone else will. While we are all hashing more for the same power. We are all hashing more. And difficulty goes sky high to compensate for this.
Would like to know what I'm not understanding here.