I'm not sure how BTV calculates those values, but as a Cardinal fan, I can say there is no way they'd trade Flaherty for Arraez. Flaherty produced 5.5 bWAR as a 23 year old and Arraez has 5.9 bWAR in ~2.5 years. The Cardinals won't give him up, he's seen as their young ace. Yes, he was injured, but he came back and pitched at the end of the season so he should be good to go for 2022.
Now, if Arraez was a slick fielding SS.......