If you're running the 4k display at 1440p, I'd agreed. But I run two 4k 60hz displays on a 16" MacBook Pro work laptop at 2880x1440 effective resolution and it looks fine to me. Yes, it doesn't look as good as the Studio Display I have on my personal Mac. But even though I have the MacBook Pro screen right next to the 27" monitors, I just don't notice the difference as I switch between them all day long.
I'm not saying there is no difference. But I suspect how one reacts to it is highly dependent on the person. I wear glasses that aren't perfectly focused for either screen, but they're good enough to get the job done - and mostly importantly, I get to use my two 4k 27" monitors to give me the same effective resolution as a Studio Display at far less money than two Studio Displays.
