Brandin Cooks is absolutely better than Emmanuel Sanders. Let's look at the facts.
Cooks
2017 - 16 games, 1082 yards, 7 TD, 16.6 YPC - 65 Rec
2016 - 16 games, 1173 yards, 8 TD, 15.0 YPC
2015 - 16 games, 1138 yards, 9 TD, 13.5 YPC
Sanders
2017 - 12 games, 555 yards, 2 TD, 11.8 YPC
2016 - 16 games, 1032 yards, 5 TD, 13.1 YPC - 79 Rec
2015 - 15 games, 1135 yards, 6 TD, 14.9 YPC
First, Sanders didn't by any means have a better season than Cooks in 2016 as you assert. Cooks had 50 more yards on 14 less receptions - which is a good thing. Anyways, he had Trevor for a large portion in 2017 and 2016 so there isn't really a reason you can say that he played worse in 2017 than 2016 because of his QB play - and that came even with the fact that he was the #2 passing option on his team. I also don't see why catching the ball in tight spots has to be relevant in this case. Cooks had far more production - despite having the consistently share the ball - than Sanders by being able to get open, and that's a great thing. Having to consistently catch the ball in tight spots isn't something that's all together necessary when you have a guy who can get separation and get open. Anyways, did you forget the Cooks catch against Houston?