> About a month back, a fellow senior manager tried stop this pattern by
> encouraging Bradley to do more remote lunchtime-meet-and-greets with
> his team **(so Bradley's budgets are spent on something other than
> training team members)**...

Taking what you said at face value. 

Trying to intentionally sabotage the growth of your junior engineers, wasting their training budget, and wasting their time, with this corporate double-speak and "social" subterfuge was a colossal mistake.

At best, that suggestion was passive aggressive and underhanded. And not only it insults the intelligence. But at worst, if it's successful and successfully slows down the skill acquisition of your engineers, then it's the equivalent of shooting your own company in the foot. 

After all, there is often a 10X differential between top engineers and bottom ones (although your top engineers are usually not paid 10 times more). And so it's in the interest of you company to make sure everyone of them gets up to speed as quickly as possible. And this growth is difficult enough on its own. You don't need to make it even more difficult. 

And instead, I would suggest you forget such underhanded tactics and offer those engineers golden handcuffs. In other words, you should increase their compensation to be competitive with the marketplace, but at the same time you should try to delay and stagger those extra bonuses over the space of four years so as to make them think twice about leaving early (otherwise, they'd be leaving money on the table).

This is how top tech companies deal with retention issues. 

> All people leaving his team, during exit interviews, seem to be using
> some kind of script where they praise him, and cite salary and
> incompetence by Bradley's boss's boss as their reason for leaving.
> This has happened 8 times. It feels very much staged.

Yes, colleagues will speak with each other. That doesn't mean there is a script. It just means that they'll often gripe about the same complaints when they're together. 

> Dealing with manager that has high turnover but great reviews from
> departing engineers

Also, I'd suggest you stop focusing on his turnover rate.

Can his team deliver and get the work done? That's the main question you should be asking. Also, is that manager good at recruiting? 

In other words, you should focus on his results. And if he gets good results, you shouldn't try to micromanage him or sabotage his efforts. His job is hard enough already.