Yes, because "
native resolution"
is a number and (if you fix the screen size, 2560x1600 is sharper than 1920x1080 or quote the native resolution in pixels-per-inch) higher numbers
do mean increased sharpness. (The FHD screen on the entry-level XPS13 is 166ppi, the 13" MacBook Pro is 227ppi - just use Pythagoras to work out the number of pixels along the diagonal and divide by 13.3")
Then you think of it wrong: that's simply not what "native resolution" means. Look it up. You're talking about "screen real estate" which is far trickier and more subjective to define, depending on the resolution, the physical screen size, your eyesight and even what software you're using.
...and that greater clarity means that you can zoom out further on your spreadsheet/text document/diagram/photo without losing any detail
so you can fit more on the screen. The detail is there, and if your eyeballs aren't up to it then the only solution is a physically larger screen. The "looks like" resolution/pixel doubling mainly affects those UI elements that you can't zoom/shrink so whether sharpness or pixel scaling has the biggest effect on "real estate" depends on what you are trying to display. I guarantee that (all other things being equal) you'll fit more (say) legible spreadsheet rows in a full-screen window on a 13" MBP screen than a 13" FHD one. (All things aren't quite equal because, regardless of resolution, the PC screen is 16:9 ratio and the Mac is "squarer" 16:10).
(a) That 1050 pixels is actually rendered at 2100 pixels internally downsampled to 1600 pixels and can accurately render more (say) lines of text than either a "native" 1050p screen or a native 1080p screen. Not as good as 2100p but way better than 1080p.
(b) I don't have a 13" MBP at hand to test, but you can Option-click on the 'Scaled' button in the displays preferences to get a greater range of scaled resolutions. Or install software like SwitchResX. You can run at "full native" 2560x1600 if you like, but Apple disables it by default because everything would be far too small for most people (but perfectly formed) on a 13" screen.