The only people who see Docker as a hurdle are those who haven't used it. Especially with these microservice apps.
I run my self-hosting stuff on lxd and nest docker, but lxd is a better fit for 90% of my needs. I don't hate throwing docker-only or docker-preferred stuff into a nested docker container, but I will almost always look for alternatives to docker-only software. That said, I fully understand why immich devs would prefer to package for docker-only and leave other approaches to the community.
I run my self-hosting stuff on lxd and nest docker, but lxd is a better fit for 90% of my needs. I don't hate throwing docker-only or docker-preferred stuff into a nested docker container, but I will almost always look for alternatives to docker-only software. That said, I fully understand why immich devs would prefer to package for docker-only and leave other approaches to the community.