FWIW when the Red Sox traded Mookie Betts with one year of team control remaining, Betts had posted 36.9 fWAR and 42.2 bWAR in 794 games with the Sox.
Rafael Devers, who has one year of team control remaining, has posted 18.1 fWAR and 15.2 bWAR in 689 games with the Red Sox.
Betts was a four-time All Star and the 2018 AL MVP while Devers is a two-time All Star who has never finished in the top 10 in MVP voting.
Since entering MLB in 2014 Devers ranks ninth among qualified third basemen with 18.1 fWAR in 689 games (sandwiched between Kris Bryant with 18.2 WAR in 620 games and Eugenio Suarez with 17.5 fWAR in 810 games):
https://www.fangraphs.com/leaders.aspx?pos=3b&stats=bat&lg=all&qual=y&type=8&season=2022&month=0&season1=2017&ind=0&team=0&rost=0&age=0&filter=&players=0&startdate=2017-01-01&enddate=2022-12-31
Newly acquired Justin Turner posted 22.2 fWAR in the same number (689) of games over that period.
Working in Devers' favor is his relative youth at 26 years of age.