I have two thoughts on the CJ "benching." Herman referenced one in his presser. The receivers aren't doing a great job in the scramble drill right now, which wasn't a big deal when Buechele was at QB but with Ehlinger it is. It's impossible to know who's falling short without seeing the all-22, but arguably they all are.
This is totally a guess, but maybe Collin's gotten frustrated with the double teams and is giving up on plays.
The more likely explanation is that it's because he's not making enough of his limited opportunities downfield. The scary thing about 6'6" receivers is they turn 50-50 balls into, like, 70-30 balls. Collin did this against USC, which is what earned him the frequent double teams, but to my recollection he hasn't done it since. When he gets single coverage — which does still happen, a lot — and the ball comes his way, he has to make something of it. He dropped a touchdown in the 4th quarter on a drive that ended with 0 points. It was good coverage and a tough catch, but that's why you throw fades to 6'6" receivers — the good ones make tough catches against good coverage. Drop enough of those — and I really want to stress that by 6'6", star receiver standards, this is a drop...
— and defenses are going to stop double covering you. Texas isn't good enough to work methodically downfield; they need more explosive plays. If Leonard gets single coverage but comes down with one or two of those deep shots, it opens everything else up, and he's giving you something that Collin hasn't been.