Theoretically, texting is faster with a flip phone. That is, if you get skilled at feeling where the buttons are without looking. I had a friend who was blazingly fast at texting with one hand, blind (even with the phone in his pocket), and he could do it while holding a second conversation. That’s not possible with a smartphone.
Sadly, this person committed suicide a few years ago. I don’t think that the two are related, but I mention it as a disclaimer, just in case…