Timing, Anticipation, and release is what matters more than arm strength.
Arm strength doesn't really matter in the NFL, it's all about anticipation. But more than anything of that, it's about trusting your receivers. Here is an example for you.
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Preston Williams is running a deep out route. Lets say on his 8th step he decides to plant his inside foot, sink his hips and explode at angle for the out route.
Tua decides to throw is before he even plants his inside foot, causing the ball to be there when he breaks out of his cut. Ball arrives perfectly on time. Its bang bang and the DB has zero chance of picking it off.
Now lets take another player in Lynn Bowden. Bowden decides to shimmy and take a giant hop step at his 8th step. He stutters for another few steps then rounds out his cut and goes to the out. Tua holds and is unable to throw because he doesn't hit his marks when Tua is ready to let go before Lynn sinks and his hips and cuts. This messes up timing and anticipation. But what it does more than anything is mess up the trust.
Tua will start trusting Preston because he runs his routes and is where he needs to be when he needs to be. When Lynn Bowden runs routes, he isn't and that messes with a QB in a bad way like Tua.
Now lets take Herbert. Herbert is notorious even in his San Diego tape, to be late on throws because of his arm strength. He will throw that out route AFTER the player makes his cut, but can get it there because of his arm. However, his anticipation still lacks immensely. But it doesn't matter because of his arm strength and it can overcome the timing issues. But he doesn't need trust because he can get the ball to his player.
What teams will start doing next year (at least I think) is start running back that Rex Ryan cover 2 blitz scheme when playing Herbert. It allows the DB's to jump and also squat on routes. Herbert really did well this year off using his arm and relying it over everything else. But watch the Patriots game. Belicheck turned up the blitz and pressure to an 11 and Herbert got flustered badly. Watch next year. Teams will start using a zone blitz defense and watch Herbert's eyes and his lack of anticipation and timing to start jumping his routes.
Anyways long story short. Tua is all about anticipation and timing. Get receivers he trusts and he could have the weakest arm in the NFL and still dominate. Because a QB that can release it faster than anyone else with excellent anticipation and trust in his receivers is impossible to defend.
