Here is another quote, and something of a warning about rules. From G. W. Chadwick, "HARMONY: A Course of Study", 1897. Chadwick was the Director of the New England Conservatory.
Quote:The dominant triad is always succeeded by that of the tonic (never by that of the subdominant), when its third (leading tone) is in the upper voice.
This is a rule unique, so far, in my recent reading. It is extremely specific, yet wrong, I think (at least, it omits any mention of the notion of deceptive cadence, which -- I think -- allows the third of the dominant to progress to the third of the vi chord).
But it is attempting (at least, by my reading) to address the problems of the dominant followed by the subdominant, and the outlined tritone that will be likely to occur.
As a result of all this recent reading (12 harmony books in 24 days), I just recently used a consciously-chosen augmented sixth chord for a consciously-identified modulation problem. Benefits, therefore, somewhere ....
Persichetti, btw, was a jerk! And a bad composer, imo. He did reputedly have an extremely good ear, however. I've never looked into his harmony book, and I'd never program any of his music, for personal reasons.