Good post, more perspective is always welcome. Plus, I always love seeing that Neo statue.
In Shars, mastiff blood does not have a positive result. It changes the dog to its core. In recent years, people presumably do it anyway for fighting purposes, but that ain't a Shar anymore. And it shows.
The reason why western mastiffs tend to destroy Shar genetics has quite a bit to do with the mountain mastiff heritage the Shar already has at its core. It's doubling up on the mastiff internally while still passing externally. The only good thing about it, if we allow to characterize it as such - is the combat aspect. The dogs will not be braver than Shars. But they will dance like Fred Astaire.
Also, if "recent years" in your sentence above stand for "from late 1980's onward", we're on the same page. Regardless of what the show world was up to, the dancing community was redesigning the breed all along.