You mean you're ok with default scaling, which is, I guess, "looks like 2560x1440"?
I'm doing "scaled" -> "More Space" which says 3840 x 2160. I opened the MacBook (which I also use "More Space" on) side by side using MacRumors in Safari as a test and I went to max zoom in the browser and that still wasn't enough. The additional zoom I get out of pinching the trackpad is the only time it is noticeable. I have 20/20 vision and I measured leaning back in my chair. It's 18 inches from my face to the screen. I have to really force myself to notice any blur in that scenario. I can read all text in any app or site without squinting or feeling like it's too small. Any "test" that you're aware of that might help emphasize it?
Caveat, I'm not a "display" person. 120hz, true HDR, local dimming, mini-led, etc. on any device phone, tablet, monitor, tv, are not must haves for me. There are plenty of people who need some of those for their professional work and others who just say they need all of that for future-proofing or whatever their reasons might be. For me I think the fact I can "see the blur" if I force myself to look for it, makes me feel good about my purchase and not paying 2x for a 5k display. The way macOS scaling gets described on the internet makes it sound a lot worse than it is (at least for 4k 27"). Also this website says retina happens at 3840 x 2160 27" at 21 inches away from the screen
http://tools.rodrigopolo.com/display_calc/. I might try that distance now, I have a deep enough desk and I'm able to read very small print at about 28" away from the screen. But even if I sit 1" from the screen it looks good.