Yeah, it's a very strange criticism. I would think the ability to put touch on a pass is something you'd like to see in someone with a big arm, as there is a tendency for qbs like that to force every throw. Same with seeing some footage of dink and dunks...again, don't you want a guy to make the smart throw?
Ultimately, he's a huge player with a ridiculously strong arm, no huge issues with his mechanics at his age, and what appears to be an outgoing personality.
He's done well in camp settings but he definitely has more delta then most prospects in his ranking category. Will he be able to assimilate the playbook? Will he be able to come off his first read and make progressions? Will he be able to read the coverages correctly? Will he maintain velocity when asked to get outside the playbook? An underrated part of Roethlisberger's game is the ability to move around in the pocket to buy some time. It's something Murphy will have to do as he's not the most mobile?
When you look at Sark's history, his best qbs aren't always those with the best arms or physical attributes. However, he's had success with all sorts. Murphy is a guy who is well deserving of a high 4 star rating. If everything clicks, he's a 1st round talent since you can't teach arm strength, size and personality.
Outside of a surefire star like Ewers, it's hard to find a prospect that has as much upside.