I agree with the OP about how the future of airline miles is bleak, but I do think that there is still value to be gained - just not what it used to be, and in different areas.

When I started in this some ten years ago, elite status was great, but the real reward were lots of miles earned, with the ability to exchange at amazing rates for easily available Business Class longhaul trips. I'd get c21,000 miles for each £300 round trip from London to California. For two trips, I could receive a Business Class single to the Far East or South Africa. Today, I earn perhaps 2,500 miles for the same trip and it costs 100,000 miles for the same ticket to HKG.

I used to deliberately lengthen trips to earn more miles; economy was relatively comfortable and I was looked after well. Today, economy is horrible - even E+ on UA is not nice - and miles are next to worthless.

However, on the plus side, it's usually possible to buy Business Class for much less than it cost several years ago, Business Class itself is much nicer and earns very well. Because economy is so awful, it has become imperative to maintain status, at least on UA, because the benefits are the only thing that make long flights tolerable.

So, my strategy has changed fundamentally. I use my miles purely as a means of buying flexible tickets where I need flexibility - and often replace these at the last moment if prices remain reasonable. In terms of earning, I focus only on elite qualifying. Once I know I'm past my targeted threshold, Norwegian or EasyJet get my business. But, getting to the threshold, I still do my best to game the system.