I'm not really clear on what is questionable here...
* that debian-mate image was the most recent until yesterday, when the 5/1 image was uploaded to pine.org
* the most recent longsleep simple image is dated 4/23 (therefore, I have his latest DTB, you know, the 2 dtb's that are loaded at 21mb and 22mb sector locations of the SD card after the ATF and SCP blobs)
as for the "os image" that you refer to, I've opened up his scripts to see what they do, which is to download the Ubuntu's core rootfs
see his script here:
https://github.com/longsleep/build-pine6..._rootfs.sh
which is ONE of the suggested ways by debian to boot an arm64 system for the first time as noted here:
https://wiki.debian.org/Arm64Port#Official_Debian_port
OTHER suggested ways of booting an arm64 system the first time at that link are to use an existing kernel, combined with debootstrab to build a rootfs
And the 3rd option is to install with the installer.
to do this, you have to get debian's netboot initrd loaded so that it can launch the installer.... this is what I did.
since, if I'm not mistaken,
* longsleep's kernel has the nic drivers built-in rather than loaded as a module...
* it's clear from his scripts that his init looks for a rootfs on part2... if found it does a switch root, else drops to a busybox shell
so, to use debian's official initrd, is NOT questionable.
Nothing I've done here is questionable.... I may have overlooked a step or misunderstood something...
but it's ALL repeatable and follows documented approaches...
that, by definition, is NOT questionable.
that being said... If I've done something wrong.... please, feel free to politely point out what and/or where I've done something incorrectly.