If he was already performing for years in t20 it’s fine to continue opening. He might need to drop from opening to middle order in Odis eventually, but we’ll make that decision if or when he does fail at opening.
Fakhar hasn’t cemented the opening spot yet in t20s. Which is why it is a problem at his age. You can’t say he can come in and perform instantly even at his age of 35 in t20s.
Honestly wouldn’t mind him opening if it didn’t mean dropping Farhan. But if that’s the result of Fakhar opening (and I wouldn’t want to drop Saim either it’s not worth it). You are messing with long term potential in t20s for a guy who we are not even sure will perform or not at 35. That isn’t worth it.