On a backshoulder throw down the sidelines, the receiver absolutely has a responsibility. It's a dangerous throw, but if your receivers are physical, it lessens the risk considerably. And when both parties do their job, it can be a nightmare to defend.
The more I think of it, I actually think a QB who can take off is undervalued. If I can't have a higher tier backup, give me a guy who can just be smart with the ball but poses a threat to gain yards with his feet.
Gimmicky? Sure. Optimal? Not at all. But when you have Dez out wide, Witten in the middle of the field, a back like Zeke who can flare and hit the flats, and a monster zone blocking OL, a dual threat QB will get his chances.
Showers can make some throws. But, and that was his rookie year, he's not going to get away with telegraphing his throws against real NFL talent, and he needs some serious work reading the entire field. Not unlike most rookies drafted in any round.
Hopefully he's progressed. If he can learn to use the weapons on offense, and keep turnovers down, he'll have potential.
I also don't question a guys "want to", especially a QB, when he gladly covers punts just to play the game.