You make some good points. I think Costa has been phenomenal for them this season and suspect they would have a few less points without him. Also I'm not sure how well their new 3-4-3 would function with, as you said, a few players missing. Wing backs can be hard to replace, as well as their star players. Think Chelsea will be too good for Brom, but for sure it will be harder for them without being able to freely counter attack an aggressive team.