DSL uses the latest Debian kernel. It is not any smaller than Ubuntu.
It fits into under 700 MB and runs in well under 100 MB of RAM. The default Ubuntu image is about 6 GB now and takes a gig of RAM.
Have you not tried it? I have:
https://www.theregister.com/2024/02/14/damn_small_linux_retu...
Try Alpine. It's amazing.
Xubuntu 22.04 took nearly 10 GB of disk and half a gig of RAM. I measured it:
https://www.theregister.com/2022/08/18/ubuntu_remixes/
Alpine takes 1.1 GB of disk and under 200 MB of RAM.
https://www.theregister.com/2025/12/05/new_lts_kernel_and_al...
Both running a full Xfce $CURRENT desktop, in a Virtualbox VM.