The change at QB is going to affect everyone else one way or another. They need to take a look at the offense week to week before making the kind of sweeping suggestions brought up.
Cooper over Tavon I actually think might help the offense. Coop has a catch radius and plus hands, Tavon's hands are mediocre at best. But that said what will Tavon do with Goff hitting him in stride? Will it add a big play or two per week to the offense? Maybe. And then of course what would need to be considered is a three wideout lineup of Britt / Austin / Cooper, particularly with Goff's accuracy added to the offense.
Higbee simply needs to be in the pattern more. He is a big target, and people are going to see what he can do starting this weekend because of Goff: I gotta think the kid is going to know where he's at and will put it up for him more often.
I think the offense is going to look better. I expect a mistake or two by Goff, but it's time to get him out there and take his lumps. On the other end of all that he will add a big throw or two that Case would not attempt. This offense will take more risks with the kid in there and that is going to be a good thing IMO.