I don't know, but I guess lots of languages have a distiction between 'be' and 'be in'. Old English did. I know Spanish and Chinese draw this distinction clearly.
"You will not fail to infer from this that an English copula is not automatically restricted ....."
I'm afraid I will have to fail to infer that. It is not a fact, taxonomic or otherwise, rather a misreading of the facts.
Philo, you seem to be saying, 'be' as a full verb is always copular. Leave aside its use as an auxiliary for now. Do you see no difference in its use in:
1) He is a teacher. Apposition. Coupling. The same apposition: He, a teacher is bound by certain rules.
2) He is in London. You would never equate He = London to say that: *He is London. 'is' looks the same in both, but there is a difference. 1) couples, equates, 2) designates location.
If a copula verb does not assert an identity between arguments, why call it copular? Just call it a verb. All verbs link their arguments, that is no big deal. 'I run fast'
English can not do without its form of 'be in', because such a verb is needed in language. If it happens to look the same as your copular 'be', don't just accept that it is, in fact, the same word.