With the hooker situation, this is the how I see it.
Farah was good his whole time out there. In the first 40 I feel he earnt his spot.
Cook was rocks and diamonds. That try showed what cook is capable off. But outside of that his performance was mixed. His defence was a shocker, very sloppy. So if its a choice between the 2 for 80 minutes you have the consider Farah's consistentency in attack and defence, over cook being capable off some good and bad, and defence not up-to 1st grade standard.
In that I'd go for Farah.
The next option is whether to play one on the bench. This isn't just a simple can cook provide spark. First you have to factor in the other forwards. The twins struggle with every minute the play over 20 minutes. Sutton has always struggled over 80 and Chricton also performs well off the bench. To waste 2 interchanges on hookers is risky with a big pack. To make it work there might have to be an overlap were both players are on at the same time. This is where it falls apart. When Farah came on cook became a wasted player. He didn't do much when Farah came back on. 2 at the same time didn't work. It's nice to say cook can come on to provide spark, but it has to do it in a way that works in the overall Team structure