Yeah, Tether isn't great. Why use that as your example? There are plenty of other stablecoins and the article was about Bitcoin.
Plus, money has been coming out of Tether and into other stablecoins and what is happening with Bitcoin's price? Yeah, up.
Which studies are you referring to?
https://www.coindesk.com/whats-going-on-with-tether
https://voxeu.org/article/stable-coins-dont-inflate-crypto-m...
https://www.sciencedirect.com/science/article/abs/pii/S01651...