I think they would be worse by a decent amount.
The two man game of Jokic and Murray has grown and developed over years. While I do think Jokic can play along side anyone I don’t think that is true of Trae. Trae has never played with a player like Jokic and I think there would be a lot lot of growing pains with that duo.
While Murray isn’t a great or even a good defender I would say he is net neutral that is still leagues better than Young. Murray is a really strong and athletic 6’4 player. That size really does make a difference on how bad of a defender you can be. Murray is also a great rebounder. We saw in the Miami series especially how big of a bonus having the smaller player in your lineup be 6’4. Taking Murray out and putting Young makes them a terrible defensive team.
Sure Young is the player I would want as my number one option out of the two. But as a number two I don’t think you can do much better than Murray.