brent System requirement are completely arbitrary and meaningless to me, personally, and I'll just talk about Solus.
I think that "realistic" depends on the user.
My 11-3180 railroad Solus Plama build is just under 14 GB (500 MB EFI, 4 GB swap, 9.5 GB EXT4). Solus Plasma OTB, remove Firefox, Konversation, KConnect and Thunderbird, add Edge Flatpak. 1 GB user data.
My normal Solus Plasma build (on the 7390 portable M.2 external) is just under 41 GB (500 MB EFI, 4 GB swap, 35.5 GB EXT4). Solus Plasma OTB, remove Firefox, Konversation, KConnect and Thunderbird, add Edge Flatpak, Zoom Flatpack, Aisleriot, Mahjongg and a few other toys. 21 GB user data.
For me, that (15 GB +/- on a minimal use computer and 40-50 GB for daily use) is what is realistic.
I can get down under 15 GB and still have a usable Plasma build for internet browsing, document reading and a small subset of my data, but I would be really hard pressed to get down to 10 GB even if I dumped the data and slashed and burned my way through the remaining packages.