Earlier quoted context omitted.
No, I don't have any data. The problem with monoculture, by the way, is that you might end up discarding somebody for "wrong culture fit" rather than actual skills. And that's something I'd like to avoid.
That's only a problem if there's a shortage of people with applicable skills, which doesn't apply to the vast majority of businesses. All other things being equal, a "good culture fit" should make a better member of the team. If monoculture improves team effectiveness, then a better culture fit is likely even worth paying a price premium.
No, it's a problem to the discarded person, too, and potentially any future colleagues they might have worked with (or even hired/fired). Hiring and firing are not zero-sum games, they impact more than the just immediate individuals concerned.
"If monoculture improves team effectiveness"
This is a big "IF" in my eyes. Everyone going to the same bar to have a good time may be great fun, but isn't it nice to have some people who prefer other work hours who can start or finish something up for a team member in odd hours? Conversely isn't it nice for the odd-hour or solitary team member to have a more group-oriented colleague who can bring things to/from the solitary person to the group session? Etc... to other specifics.