Thanks Gianluca. I actually discovered the metric compatibility issue shortly after writing this post. I had started a follow-up, but never got around to finishing it.
That makes it a tricky issue. At least it’s reassuring that some thought went into these decisions.
Nevertheless, the Liberation substitutions are not the only ones at fault here for glyph incongruity. I would like to see more thorough and robust substitution rules. But then again, maybe there’s some other issue I haven’t considered. Would love to have a long conversation about this with someone who knows the whole story.