No. This is a different thing. The problem is when people haven't coded their CSS correctly and assume default background is white and then set a non default foreground of black or something. Those sites will still break for dark themes even with this API.

In fact, if people actually understood the first C in CSS, this thing wouldn't even be necessary.

Dunno why you're being downvoted. This indeed is a very widespread problem. Even some Google services (like Google Docs) have it.

It generally happens when the site specifies the forgeround or background color but not both, leading to very low contrast.