> It used to be the case that speaking in that register was a strong signal of a social pedigree and an expensive education.

It's not the same register. There's a vast difference between the extemporaneous speech of the old school patricians and today's C-suite corp-speak.

Here's Robert F Kennedy Jr. speaking off the cuff at a public event moments after hearing that MLK had been assassinated: https://www.youtube.com/watch?v=A2kWIa8wSC0&t=238s.

That's the speaking style of social pedigree and an expensive education. You'll tend to find it contains lifts of poetry, like Kennedy's evocation of Aeschylus, and little reference to 'synergy', 'collaboration', 'efficiency', etc.