With teams running multiple TE sets many have several TEs
I think the Cowboys utter waste of resources is well established and made clear. We don't need to rehash that here. But suffice it to say that if they can keep 4 TE's on the 53-man roster, they could keep 3 QB's, especially given the obvious need.
but we're talking QB and there's only so many opportunities even in preseason to see all your QBs play. If the Cowboys draft a QB high they're going to want to see a lot of him in preseason because they're not going to get much work once the regular season starts. You bring in a veteran QB and have them duel it out in preseason with your high draft pick giving both QBs equal opportunity with some of your starters. To have a fair competition all your QBs need time with the starting OL.
If you've got a reliable backup, you can keep the rookie in bubble wrap for a season and focus strictly on learning and development. There's absolutely zero need for any sort of "competition" involving the rookie at all. Ideally, you don't want to play him unless you had to.
Your young QB is going to need the most work and because of their draft position they're going to get a lot of work during the summer reducing the reps of the other veteran QBs so you have to settle on one veteran QB to compete with your young QB. If the Cowboys take a QB in the "first round" I don't see them entering camp with 2 veteran backup QBs especially a couple who flamed out in Cleveland. You don't draft a QB in the first round and have them compete with 2 veteran backup QBs.
I'm not talking about the rookie competing with any veterans at all. If you're taking a guy at #4 overall, his place is secured for several years. And a guy like McCoy, who I'm advocating the team to sign, is enough of a veteran to not need a huge amount of reps anyway. Given the situation in Washington, he's certainly used to that.
As for Manziel? He'll take whatever he gets and make the most of it to show he belongs, or he won't. Part of any conditions I would have is that he is on a zero tolerance policy. If this is "where he wants to play" he has to prove it by being a model citizen. Or else he's gone and his career is likely over. I'd make sure that was crystal clear to him and I would stick to it. If Jerry doesn't do the same, that's on him, not Manziel.