A single anecdote of a misguided manager ruining it for their team does not invalidate the idea of T-Shaped people.
At least that's how I understand it.
Unlike generalists, they have gone through the tough process of going very deep into something. They understand that there's a lot of detail under the surface of any domain and they know how to get there when needed, whereas a generalists would disregard or be ignorant of any complexity.
In my experience these people are definitely better managers (unless they suffer of old physics prof disease), but I don't see the large benefits for more specialised roles. The more I switch to being a generalist, the less I can actually deep-focus, and talking to friends and colleagues, it doesn't seem like I'm the only one.
That said, interest and curiosity about other fields, especially the ones you actively work with or neighbour is probably always a great quality to have.
I'm not really clear if David Epstein merging the two ideas is the 'true' idea of T-Shaped people in the hive mind of the internet or not.
tldr: T-Shaped could include multiple specialties (which make it not look much like a T)