exactly. plus i mean, this particular build is quite boring because it's, like i said, silverblue. vanilla gnome and all that. but one can go quite wild and make vastly different builds. building locally takes very little since it's basically decompressing a bunch of packages, moving some files around and building an initramfs, so the infrastructure one actually needs is minimal (especially if said upgrades happen silently).
i must say that even though this tech has been around for a while it's still very much WIP. much of the ostree command line is undocumented, some commands are hidden and even though there is significant overlap between rpm-ostree, ostree and bootc, they do quite different things and some things are easy with one tool and outright impossible with the other. but personally i think this is the future of "mainstream" linux, and even though "immutable linux" has been often associated to locked platforms (e.g. android), it's been fun to showcase how you can do it yourself too, with whichever distro you like.