In the past year difficulty has increased by 13x (source: chainradar.com 1 year chart) and price has increased by 19x (source: coinmarketcap.com 1 year chart) while the block reward has decreased by 40% (source chainradar.com 1 year chart, also emission formula). Putting this together:
19 / 13 * (1-40%) = 0.87
Meaning revenue with constant hardware and power costs has dropped by 13%. Maybe significant but hardly 'dramatic'.
That's probably consistent if not smaller than the rate of technological progress (better CPUs and GPUs), meaning there is no real decrease in profitability assuming regular hardware upgrades.
This is frankly much ado about nothing. Hash rate of successful coins with increasing prices will always rise, and when the price rises a lot so will the hash rate.