Resolution is the killer for that application. The panels in the Vision Pro are dense, but through the distortion of the optics and with those pixels stretched over your entire field of view only a fraction of them will actually be displaying your virtual monitor(s), and as you scale a monitor down in virtual space it also becomes lower resolution. For comfort and ergonomics you don't actually want a giant monitor that fills your entire FOV, there's a reason why real monitors have settled around 27-32" despite larger panels being available.
Ironically existing Apple users are the most likely to notice this limitation, since their computers have had very high DPI displays as standard for a long time.
23 million pixels, divided by two, makes 12.5 MP per eye. Let's assume it's nearly square, so taking the square root gives us 3535 pixels in height and width.
This graphic claims 3400x3400 resolution, so we're not far off:
Frustratingly, the spec sheet doesn't list FOV, but let's assume it's on the order of 110 degrees. That gives us about 31 pixels per degree.
Right now, I'm sitting about 30 inches from a 24" diagonal 1920x1200 monitor. That gives a vertex angle of about 45 degrees, and it's 2264 pixels corner-to-corner, so I've got 50.3 pixels per degree. That's not high DPI, but it's acceptable. I also have a 4k, which is lovely, but given the chance I'll take more real estate over a small, high-DPI display. And with Vision Pro you can put monitors anywhere.
Another detail to consider is that your 24" monitor is probably benefiting from subpixel font rendering effectively tripling the horizontal resolution of text, but that can only work on a pixel-perfect display, not on a virtual display which is scaled and transformed before being displayed on a real panel.
I agree low DPI monitors are still acceptable, I'm using one now, but that's really contingent on subpixel fonts.
I don't personally use Apple products, but I do have some trust that they can get font rendering right. The browser window I'm looking at right now is a subset of my monitor, and could be considered a 'virtual display', but subpixel rendering works in that region. There's no reason other than laziness or lack of vertical integration that it wouldn't work in a virtual environment.
Keep in mind that the lens distorts the pixels so the density is not uniform across the FOV. Word is the PPD is 50-70 in the center, and beyond 60 is not visible.
Ironically existing Apple users are the most likely to notice this limitation, since their computers have had very high DPI displays as standard for a long time.