There are still growing pains, but https://github.com/osbuild/bootc-image-builder exists and is likely to become exactly that in the general case (as it already is for the redhat family).
Oh those size limits are pushed plenty by AI images, no worries. I recently had a good laugh when I found a docker image that was 2 - 3 times as big as the OS partition of a lot of our smaller servers.
And our OS image build order would reuse layers better than those.