I mean, it's probably a good idea to have them higher, given that if someone wants to use it with some typical out-of-the-box desktop settings, that's not unreasonable, but while I haven't looked at the Ubuntu installer for a while, I strongly suspect that it permits you to do a minimal install, and that all the software in the Debian family is also there, so you can do a lightweight desktop based on Ubuntu.
My current desktop environment has sway, blueman-applet, waybar, and swaync-client running. I'm sure that you could replicate the same thing on an Ubuntu box. Sway is the big one there, at an RSS of 189MB (mostly 148MB of which is shared, probably essentially all use of shared libraries). That's the basic "desktop graphical environment" memory cost.
I use foot as a terminal (not in daemon mode, which would shrink memory further, though be less-amenable to use of multiple cores). That presently has 40 MB RSS, 33 of which are shared. It's running tmux, at 16MB RSS, 4 of which are shared. GNU screen, which I've also used and could get by on, would be lighter, but it has an annoying patch that causes it to take a bit before terminating.
Almost the only other graphical app I ever have active is Firefox, which is presently at an RSS of 887.1, of which 315MB is shared. That can change, based on what Firefox has open, but I think that use of a web browser is pretty much the norm everwhere, and if anything, the Firefox family is probably on the lighter side in 2026 compared to the main alternative of the Chrome family.
I'm pretty sure that one could run that same setup pretty comfortably on a computer from the late 1990s, especially if you have SSD swap available to handle any spikes in memory usage. Firefox would feel sluggish, but if you're talking memory usage...shrugs I've used an i3/Xorg-based variant of that on an eeePC that had 2GB of memory that I used mostly as a web-browser plus terminal thin client to a "real machine" to see if I could, did that for an extended period of time. Browser could feel sluggish on some websites, but other than that...shrugs.
Now, if you want to be, I don't know, playing some big 3D video game, then that is going to crank up the requirements on hardware. But that's going to be imposed by the game. It's not overhead from your basic graphical environment.
I'd also be pretty confident that you could replicate that setup using the same packages on any Debian-family system, and probably on pretty much any major Linux distro with a bit of tweaking to the installed packages.