I guess if I had a QB formula, I might give rushing TDs less weight. I would never discount it entirely, or even close.
Just me.
Part of the reason is because everything the offense does is attributed to the qb. When a back the runs the ball for a wide open td, the qb called that. He could have just as easily done it himself if he wanted. Cam could have 15 rushing tds every year if he really wanted.
But a passing td is something that’s identifiably related to the qb’s talent, and not constructed by what formation the defense is in or who he has in the backfield with him. Tougher defenses make it harder to throw tds, yes, but that’s why Rodgers and Roethlissberger and Brady creep ahead of the pack in that stat. Because they’re beating defenses at a more consistent rate. Because Russell Wilson is leeching rushing tds from his backs means he’s better at quarterbacking his football team?
The ability to run it in when there’s nothing there is definitely a valuable stat. But when your running and passing tds are less than the next guy, what does that tell you? When you’re passing TDs are 10 or more less than the next guy, it shows lack of big play ability. I doubt Dak is running in 60 yarders. It’s also less likely he’s throwing 60 yards when he does have double digit fewer passing tds than Wilson, than Wentz.