Goff did not prove he was going to be a good NFL QB.
What did he prove was: 1) tough, 2) never blamed anyone 3) never lost heart 4) didn't turn into a deer in the headlights despite being constantly crushed 5) showed consistent emotional stability, which is a must if you are going to lead a football team.
As I said in my post to start the thread: I'm not sure why anyone would question his arm. He stands tall in the pocket and delivers a good ball. Not a canon, but plenty of velocity.
Now this year he has to improve.....a lot. He needs to get bigger and stronger and he needs to improve the mental part of the game: pre-snap reads, feeling pressure, speeding up his progressions, decision making.
No reason to think he won't. He did every year in college. He's a smart guy to begin with. Comes from a Pro sports home background. Has the physical tools.
But, in the end it is the intangibles that makes an NFL QB very good or great. Perhaps two of the greatest of all time are Peyton Manning and Tom Brady. They aren't exceptionally big or strong; neither has a canon for an arm. No one has confused either for a Rhodes Scholar. And neither can run a lick. But they process information fast; have a great instinct for the game; can bear down and rise up to another level when needed; great leaders; ACCURATE with the ball; good decisions and judgments on and off the field. But........they were fortunate to have good coaching and good teams surrounding them. Coaches that designed offenses around them to accentuate the positive and reduce the negative as much as possible. No read options for them. No QB keepers. Rarely even the "moving pocket". They make their living on short to intermediate routes and let the WRs/RBs/TEs do the running after the catch. They demand that the Oline do their jobs.
Not at all comparing Goff to those 2 all time greats.
Just saying that there's a lot that has to come together for a QB; some on him, some on others.