Note how both frames are now bold. Please note the mode-line face as
well. I'm not changing the face there. The incorrect weight selection is
also affecting the face there.

Indeed, it seems that any font weight which is within "100" in the
weight table can be susceptible to bad selection. Commit
1b2511fa2aed460120a36765ba16c14e355eef1d by itself makes sense. We
likely have a problem elsewhere.

Maybe font_sort_entities is not sorting the matches correctly by weight,
or we are calling it wrong in some places.

Cannot go further at the moment.