With the addition of non-free firmware in Debian ( so better hardware compatibility ) and the rising popularity of Flatpak and Distrobox ( so access to newer software ), the advantages of Ubuntu are narrowing and the problems with Ubuntu continue to mount. Basing something like Mint directly on Debian makes sense to me.
I have been considering trying Debian with Distrobox / Arch to fill any application gaps. LMDE might fill that void instead.