Baffling Grammar Advice Dissected

I just love it (see post below) when amateur grammarians and the real ones start quibbling. Here from Zwicky at Language Log is criticism of the baffling grammar of Brian Garner, the grand poobah of legal writing:

Garner's Dictionary of Modern American Usage (Oxford, 2003) warns against relative pronouns with possessive antecedents. Simplifying Garner's example from real life: "There may have been inimical voices raised among the committee, such as Nikolaus Esterhazy's, who just then had had an unpleasant brush with the composer." I am as unhappy with such examples as Garner is. (The history is complex: relative clauses with possessive heads are a survival from much earlier English, and are occasionally to be found in recent times, but now strike most readers as at best awkward. Things are even worse when the possessive has an overt head: "Nikolaus Esterhazy's voice, who just then had had an unpleasant brush with the composer, was especially strong." Still worse: "Nikolaus Esterhazy's, who just then had had an unpleasant brush with the composer, voice was especially strong.")

Ok so far. Such relative clauses are fairly often deprecated in the advice literature. But Garner doesn't stop there; he goes on to say that the proscription is necessary, citing a more general proscription, with an explanation for it:

The relative pronoun who stands for a noun; it shouldn't follow a possessive because the possessive (being an adjective, not a noun) can't properly be its antecedent.

Eek. Now Garner has invoked the Possessive Antecedent Proscription (which he does not otherwise seem to espouse) in its full power, and he's set himself against innocent bystanders like Mary's father adores her. The problem is that if possessives are bad antecedents for relative pronouns because they are adjectives -- they aren't, of course, but Garner thinks they are -- then they're also bad antecedents for personal pronouns like her and she. That's SERIOUS collateral damage.