@Eric:

Not that well-versed with Roots, though the biggest difference appears to be their inclusion of a CSS Grid.

Surely that’s right for some people, but my focus was as bare-bones as possible.

Based on Starkers, there are things that I’ve even removed from that, and things I’ve added from beyond Starkers & BP, because they make sense to WP (like removing the WP version, etc.).

Sorry I couldn’t be more helpful,
Atg