I don't see why your focal point is on the productivity of miners.
It doesn't matter how many miners are mining, as long as there are still miners. BTC are being generated at the same rate no matter what.
BTCs may generate at the same rate but, as it takes more and more to generate them it is not worth it to mine. Miners cashing out is the problem. The more miners decide, I'm done, the more pressure on BTC.