So what's the takeaway from the anecdote here? That Fazlur Khan should have returned to Bangladesh?

I think the usual counter to this argument is that rather than being the best & brightest, he's a product of his time, place, and circumstances - if he were to remain in Dhaka he likely may not have been noteworthy. We really don't know one way or another.

If you look at the guy who would be a top experimental particle physicist in the West and leave him in Dhaka you don't get great experimental particle physics; you get a mediocre accountant with dreams of particle physics.