Yes, that repository now carries the MNT specific patches in branches named after the kernel version for which they have been rebased.
What hassle are you facing with it? The advantage of having the dts as a patch is that it is now possible to have different device trees for different kernel versions instead of trying to have one device tree for all versions.
The dts patch is not part of the patches provided in the reform-debian-packages (as far as I could tell). I extracted the script that build the dts patch from build.sh in reform-debian-packages. But this extraction needed to be maintained. Now with the single git repo the patch is already applied and thus much easier to maintain. ~170 lines of code less: mnt/reform: linux 6.19.6 -> 7.2.6 by leifhelm · Pull Request #2064 · NixOS/nixos-hardware · GitHub