Count the pixels! Percentagewise, the window decorations and menu bar in that screenshot take up a lot more space than the modern equivalent does at 5K. If you're comparing it to to the current 14" Macbook Pro, it's closer, but Macbook Pro still wins - and still continues to hold its own even if the classic Mac is producing a 1280x1024 display. And this even though the Macbook Pro is the space-constraised pocket version! (Also note: you haven't even investigated the scaled display options yet)
Disclaimer: I have a desktop Mac, and I'm assuming the pixel counts are the same for the laptops.
(The window corners weren't always round, but there was a bit of rounding to the screen corners there from day 1: https://infinitemac.org/ - this really struck me when I first saw it, coming from the Atari ST.)