>Are there any hacks that can convince macOS (or the older versions of OS X described in this article) not to treat the display as HiDPI? Yeah, I realize the machine will abruptly feel like it needs a magnifying glass to use, but in a pinch (laptop on lap <2ft from eyes) it might work for some (insert standard disclaimers here about eyes being non-replaceable and needing to last the distance).

macOs already supports several resolutions higher than the standard 1/2native which is what Retina uses (half the native pixels at each dimension for twice the resolution).

IIRC, already the "default" resolution on newer MBPr with the touch strip is higher than the 1/2native (that used to be the default on retina laptops).

There are also apps like: https://www.thnkdev.com/QuickRes/ and http://www.madrau.com/ for more flexibility and full-native resolution even.

That said, the full native retina resolution on something like a 15" screen doesn't make any sense to me except for some special circumstances (maybe 4k movie viewing, but doesn't that already use the full resolution?).

>The late-2015 21″ iMac is ~$1.5k+, and "has a multi-core Geekbench score of 5623." Then the late-2011 17″ MacBook Pro which is ~$1.3k checks in with a "9240 Geekbench score". Is there some datapoint I'm missing here?

Yes, one is a GeekBench 3 score, the other is a GeekBench 4 score. Scores of 3 and 4 editions of the GeekBench suite are not comparable.