I have a just-turned 13 year old granddaughter who is quite the volleyball player. She has played AAU club ball since she was 8 and has always been one of the best. Going into the 8th grade, the local High Schools want her to play for them. She can because she's home schooled and it is allowed.
She's already practiced with the JV, and is probably the best player.
Yet, in the wisdom of the coach, he doesn't want to promote her too quickly. She is already pretty confident. He wants her to compete for awhile in order to prove not just to herself but to the others that she belongs, even though to most eyes she may immediately be one of the best players on the Varsity when she's moved up.
Her father is in complete agreement. I really like that.
So, yes, coaches play little games. They walk a line that makes good players who are clearly better than the others STILL have to earn it and one way you do that is to give others a shot even if it is unlikely the others can win the starting job. And partly it is because he wants that message to come across to everyone loud and clear. You must compete; you must do your best every time out. You must win the job. You get playing time according to merit; I don't care who you are. You can be replaced.
I think that is pretty much what McVay is doing. Goff is better than Mannion. But Mannion is still going to be given a fair shot to compete. It makes Mannion better, it makes Goff better. And it makes McVay a pragmatic and fair guy in the eyes of the players who know that if they play better than even the first pick in the draft, they'll get the start. And what player doesn't believe that they can win the starting job if given a fair shot? It's just the nature of the beast.