I don't believe any significant number of people buying Bitcoin are using Tether. Tether was aimed at the exchanges, institutional level investers, and day traders that wanted to move between dollars and crypto without creating taxable events (this loophole has since been closed). Its primary purpose was touted as allowing exchanges to move US dollars between themselves quickly and without using the banking systems directly.

Things may have changed in the last two or so years though, so maybe Tether's role radically changed.