Parallel Downloads Of Flatpak Runtime Platform and SDK are bandwidth inefficient
Flatpak runtimes are a subset of SDKs and ostree should be able to minimize the amount of bytes downloaded by deduplicating identical files. Builder's automatic SDK downloads get both runtime and SDK at the same time and thus are unable to take advantage of this, resulting in larger downloads, more time and a longer wait to get hacking.
Ideally we would serialise flatpak runtime downloads where the first two components are identical (I'm not sure about which order would strictly be better, but it'd be worth testing).