Default fonts with broken font-variants

Hi CSS folks,

I was playing around with font-variant-numeric and discovered that the
default serif and sans-serif fonts on Windows 10 show all numbers in
numerator-mode when you ask for diagonal-fractions:
https://crbug.com/1154042. Working around this as a page author would seem
to require me to enable font-variants based on the state exposed by
https://drafts.csswg.org/css-font-loading/.

What's the "right" way to handle this? Have page authors change styles when
their webfonts load? Have browsers special-case known-bad combinations? Add
a declarative way to use different styles for different fonts?

Has this group done an audit of any sort to figure out which font variants
are usable in which contexts? The spec mentions that "it's not suitable for
use as a paragraph-level style" in an example, but I can't find a normative
statement about how these are actually supposed to be used.

Thanks,
Jeffrey