*flashes in for a brief message board appearance*
Why would the Redskins bring in Colt Mccoy, to shop Kirk Cousins, and then if they are successful, go get a number two?
That seems silly to me.
Look, if you are on the side that they brought Colt McCoy in to allow them to allow for a trade of Kirk Cousins if it arises, you CAN'T say with any certainty that they didn't bring Colt McCoy in to be the second QB, not in my opinion. They don't likely want to go through the rigamarole of finding another number two even later in the offseason process, if they DO get rid of Cousins. IMO, they're going to have McCoy be the backup if that happens.
And they'll likely only move Cousins for a second or 3rd round pick, so they can grab a quarterback that is serviceable there or anywhere else in the draft for a 'camp arm', so that isn't ALL Colt McCoy was brought in to be either.
I think the truth of it is, that you are ALL right.

1) Colt McCoy WAS brought in to be 'an arm' at camp.
2) An arm that is significant enough, that he CAN fill the number two role, if a good deal for Cousins pops up. He has career NFL starts under his belt - he qualifies, I assure you. You may not think the world of it, but there isn't much to suggest that he's much less capable than Kirk Cousins, is there?
3) if they don't get a deal, and they keep Cousins, not only do they have an arm at camp, but they have a soft enough contract that Colt can fill the clipboard carrying 3rd QB role. This guy isn't here to disappear either, so he has something to prove - even if its just that he has a good attitude, a good work ethic, and the desire to try and keep working for a shot... here OR somewhere else.
Cousins is a decent backup for sure - so i am sure that the Redskins will want to see a pretty high draft pick to run the risk of going in another direction at backup quarterback - after all, quarterback number one DID have pretty significant knee surgery.
Just one more thing to think about... if you concede that the backup in Washington IS more significant because of Bob's injury - then how do you not also at least think about the fact that another coach may not share the Shanahan philosophy of just two quarterbacks on the roster? After all - it's a rough game out there. if Gruden differs in that, and that alone - it's justification for Colt McCoy being signed JUST TO BE THE NUMBER THREE GUY.
So you see... maybe you can't figure out which one of you is correct because you're trying too hard to be the one who is "right". Personally, i think there's an element of truth to all of the scenarios. And if that weren't true, then it wouldn't create any extra "market value" for Cousins, because the other teams GMs would just see McCoy as window dressing.
That's what makes the Colt McCoy signing such an excellent one, in my opinion.
2 cents
Sean Taylor was one of a kind, may he rest in peace.