My totally amateurish opinion is Cam might be worth 1 more win in September and October. After that, assuming Mac develops as expected, it's either a wash or the edge goes to Mac from November onwards. So to me it'd be a no brainer to just start Mac week 1, since (according to my own personal logic anyway) it'd give us a better chance to win games down the stretch and in the playoffs.
From everything I've seen & heard Mac is very close. Neither are running away or lapping the other one but Mac looks the part in terms of what we want from the position and is actually better in a few areas (getting the ball out/release, touch, I'd argue pocket movement as well) Whether you look at them, just today, no past history or include it. Mac has looked a little better imo.
I'm not holding him back simply to do it. Everyone that's objective and knows this team, understands Bill's preference. He prefers vets, he wants to know what he's getting / no surprises, don't turn the ball over etc
At the same time it's more than obvious Mac is being "fast-tracked" by Josh & others. This has been clear to me since we picked him, this was a Josh pick. They haven't just worked together, Josh seems invested imo.
Also the team is perfectly set up for Mac. Obviously QB's have different needs, strengths, concerns etc. He needs a tight relationship with his OC to start out. Him & Sark had a nice relationship. You can tell there's a mutual respect there. Whether you like Josh or not, he's established. Definitely has his faults but he's made a lot of **** work that others couldn't. Albeit with Brady & Brady > Bill, Josh but JMD made it work and maximized a lot of strengths here. So he has a decent guy to lean on.
He has multiple security blankets that are perfect for his field distribution. Mac was probably the best, easy top 3 QB in terms of targeting/hitting the MOF. Henry, Smith, Meyers & co all should feast there. I love how Bourne works the sidelines, seemed pretty crisp at the top of his routes. Agholor is who he is but he certainly can make big plays. Is versatile, you can play him inside/out. Love his potential to stretch the field from the slot when we're in 12 personnel.
Of course the OL/Running game.
Injuries are the only thing that would hold me back. I wouldn't start Jones on any team. He needs a lot of help, like all QB's, yes but I wouldn't start him if I had a lame a shakey OC, shakey OL or no targets. I wouldn't just throw him in the water no matter what.