Cubs: Biggest difference between the two comes defensively
If there is one big advantage the Cubs have in having Pederson over Schwarber, it’s versatility. Over his career, Pederson has played all three positions of the outfield. Mostly center, but that will be taken by Ian Happ so expect him in left where Schwarber was with Jason Heyward in right most of the time. Unless Ross does not want too many lefties against a lefty starter and Pederson will either platoon or could take some time in right with Kris Bryant (if he is not traded) in left. Plug him in anywhere and he can do it.
Schwarber on the other had has played all but 14 career innings of his outfield career in left. He is either going to be a left fielder or DH most likely going forward, unless the Nationals work with him to be more versatile. Regardless Pederson already has that edge. There is no doubt that Pederson is the better outfielder here and his versatility adds a lot of value to his game.
Pederson had a really good defensive year in the outfield in 2019 with 12 defensive runs saved and a UZR/150 (ultimate zone rating / 150) of 13.2. Schwarber is never going to reach that level of effectiveness in the outfield. Remember that Pederson is much quicker and agile than Schwarber and that is going to help the Cubs out both in the outfield and on the bases.