Yes, agreed. This is fair game and nothing is ever promised. Below is an interesting video that might shed light on the rationale behind recent (and other) devaluations at SQ.
Of course, the airline has a prerogative to run their business any way they want. Consumers need to come to terms that SQ doesn't just think about the redemption rates and the different levels in isolation like a bean counting exercise, but actually has a strategy for how miles should ideally be used in their view (yes, for cash offsets, exchanging for things on Kris+ and getting people to redeem at advantage and access rates). Often, this ideal clashes with the way miles bloggers have, in the last ten years, educated the public about FFPs.

The state of the game now is just another evolution in the tussle between airline and consumers - I'd say quite a bit less favorable to consumers (not just with the hard devaluation, but the stealth devaluation through restrictions, access tier (effectively a new redemption rate), and reduced award availability). To some, maybe SQ-styled luxury is just worth the splurge, at whatever cost, to amass even more miles, fly with the airline more often; to others, there is a point at which the cost of spending all that money and acquiring miles through credit cards etc is just not worth it anymore. And both (and more) positions are okay!

Personally, I wouldn't say that I have divorced myself from SQ completely, but competition has made me realize that there is another world out there, that isn't half bad. Try different airlines if the math is not in your favor, and there might be some nice surprises.