This is very misleading. Exhibit A: the warnings in question have been present for 5 years and the projects that end up triggering the warnings have not been removed. I don't know when QL started building with an ASDF version that produced the warning, but the absolute latest would have been Feb, 2021.

The full story is that there is a sub class of warnings called style warnings. Any warning that is not a style warning is typically called a "full" warning. Full warnings do break compilation by default (the spec even mandates this). Style warnings do not. That is why ASDF typically starts the deprecation process with style warnings.

However, the bad system name warnings do not happen during compilation. It roughly happens during configuration time (as ASDF is building its plan). Since this is not compilation, neither the spec nor QL care about the specific types of warnings produced. That's why the bad system name warning is a "full" warning.