Interesting you like Manaea - 30 years old with 11.6 career fWAR - over Paxton, a 33yo with 17.6 career fWAR. They’re actually very similar pitchers in a lot of ways.
Now Manaea is younger and currently healthy, but also only available for one year. The Sox could easily have Paxton for 2+, and for much less than Manaea will command.
I was surprised the Sox didn’t get any of the Oakland arms, especially once Sale went down. Now I don’t know if they tried to get any of them and what Oakland wanted in return, which might answer why. I mean, I wouldn’t deal Yorke for Manaea, but that doesn’t mean it isn’t what San Diego asked for…