It's a bizzare complaint because the show's B-Plots are these side character stories. Throwing in a useless fetch quest for Shadow is going to take up screen time. Right now Shadow's involvement in the show is tied to the A-Plot and he takes up Sonic's screen time to push that story forward. But if you want to suddenly give Shadow a quest (that's exactly the same as Sonic's, but with a different McGuffin) then you're going to either expand A's focus and runtime and reducing the current B focus or make Shadow the B-Plot moving forward. So which is it?