There is tooling in Debian to use systemd-boot, it even integrates into the upgrade process so that your boot menu always points to the current version of the kernel.
It is not default; you would need to bootstrap Debian yourself instead of using the installer, but it works. Bootstrapping opens additional possibilities like choosing btrfs on LUKS and suspend to disk. My previous Gentoo experience was very helpful.
For a long time I considered Gentoo the best, because I know my things around there. A month ago I said goodbye to my last Gentoo installation in favour for Debian trixie (the next stable release). Gentoo was too time consuming despite the binary repo.
If it would be my job to maintain a Gentoo system I would gladly accept, but there should be a need for it by the users. Otherwise I would just recommend Debian stable or Fedora.
My favourite is Debian over Fedora, because I often don’t need the latest versions of a software. And there is flatpak.
This lets Gentoo look like a beginner/user-friendly distro next to NixOS.
The fact that my OS should not be a project anymore made me switch to Debian instead to NixOS. But I need to try an immutable distro some time.