Shitty 4k displays have been cheap for a while. It's not a reasonable comparison. (My no-name brand Korean 27" IPS display was great until it frizzed out after 9 months.)
Dell's 24" UP2414Q is an IPS 4K monitor with 99% AdobeRGB and 100% sRGB coverage, and it has a 185 PPI panel that I'd argue is already in the "retina" range. Although with its ~€555 price it's not exactly in the $300-$500 range, but it's a close call, so I wouldn't call all 4K monitors around this price range "shitty" at all.
Update: it works in 60Hz @ 4K.
It was twice as expensive at launch, though. I suspect the new Dell model will follow suit.
You can buy a good 24" display for a lot less than a similar 27" display. That's a whole different discussion.
Sure, but we weren't discussing screen sizes, we were discussing 4K monitors in a certain price range.
You could buy quite a few shitty 4k displays for the price of one of these, though. Enough to get one that escapes the bathtub curve, certainly.