All displays from Apple have different resolutions. Natively they are comparable to previous Apple displays of half the linear density (800x1280-ish for 13”, 1080 for 15” and so on).
Okay, so you can "see the difference" (positively, I assume?) of this to a 27" 4k monitor.
What about 27" 6k or 14" 4k?
Side rant: Yeah, apple makes great stuff, but the naming is obnoxious. It is not "hidpi" it is "retina", not "high refresh rate" but "promotion" and then you have to look through the marketing material to figure out how '14" retina' compares to a normal UHD+ display.
If I can see the difference I would assume I will be able to see a difference between 27" 4k and 27" 6k.
My canon 80d has a resolution of 6k x 4k.
I also can perceive the sharpness of text.
I don't mind to not run 8k IF driving the display pixels consumes too much energy. The argument of Performance though should not really exist. It's much more pixels true but there are plenty of technics to separate this technically.
Even on gaming they have adaptive rendering but the display resolution itself stays the same.
The power consumption is not so much on the gpu side. Denser pixels require stronger backlights because less light gets through. So even if you were to run the screen at half the max resolution, you get worse battery life. Similarly, oled is awesome tech, but high brightness requires more energy than led backlights.