de Vries was a "twisted mentat" because he was designed by the tleilaxu to be so. I think there were suggestions that Yueh was, too.

That doesn't necessarily mean they were grown in tanks, though, they could just have been "groomed for purpose" in the same way the Tleilaxu's matriarchal counterpart the Bene Gesserit did.

(The Tleilaxu are to me a very obvious stand-in for "patriarchy": there are a few men ruling over a genderless, fluid workforce, and women are literally just birth machines.)