I'll never argue JBJ is better than Betts on deffense, but with a park like Fenway, having JBJ and Betts id CF and RF puts us at a huge advantage on defense. Even on the road, I'm not sure any team has a better one-two defensive punch at those key positions.
Yes, we can replace JBJ with some other FA, but most FAs will be about the same age as JBJ, and if they are close to him in skill level, they will be just as costly.
I'd like to lock up Betts and JBJ as long as the numbers aren't way way over board. Bogey is my "one man out", if I had to choose, and I think we will, if we want to keep Chris Sale around.