Defenses and their coaching see what you are good and bad at, and attempt to make you do the bad things. It's up to the QB and his coaching staff to scheme to do the good things. If you can't do the good things on a consistent enough basis to be a good team, you are not long for the NFL.
It's really that simple.
I've been a Justin Fields apologist, and I still don't think he's been given the right tools to be successful, but we aren't frustrated that he's only passing for 250 yards a game instead of 300, we are frustrated because he isn't even hitting `175 yards a game passing. He does seem to miss open windows while he's holding the ball. He does seem to take a lot of unnecessary sacks. He does fumble a lot even though he knows he's going to get hit. I really wish he was available for this Charger game. I would have liked to see what he can do against the 32nd ranked passing defense in the league.
If he's going to secure a future, it has to be on his return. I'm growing more and more skeptical he can do it now.