I think proof of this is that while the Ethereum prices has been dropping we are seeing network hashrate continuing to be added at a feverish pace.

Looking at the Etherscan website we can see: Highest Avg Hashrate of 268730.4354 GH/s was recorded on Friday, March 16, 2018.

This would be crazy to be simply normal miners going out and buying more overpriced GPUs while profits are plunging, but might make sense if it is from new ASICs which are way more efficient.