2. Their rotation is weak
If the rotation was at full strength and every pitcher was pitching to their potential, then I’d be confident with Cueto and Samardzija being the two best starters on the team.
I’d feel much more comfortable with three veterans in the mix, counting Bumgarner.
That way, even if only two of them perform as expected and one of Webb or Beede has a solid year, the rotation has three solid starters to help anchor the pitching staff.
I don’t believe that the team will be able to land a premier starter through free agency, so I think Bumgarner makes the most sense because he’s been with the team for so long and has such a proven track record.
There won’t need to be any adjusting to the cool San Francisco air or any culture shock. He’s been there, done that, and knows exactly what is expected of him.
Beyond the four guys who I feel are locked into rotation spots (Cueto, Samardzija, Webb, Beede) there is not a ton of depth. Dereck Rodriguez could have a bounce-back year, but 2019 did not inspire a lot of confidence for that possibility.
Just to provide a measure of stability to the rotation, I think it is essential that the Giants retain Bumgarner. Not only is he the ace, but he adds much-needed depth to a weak rotation.