I think I roll the dice on the upside. He is healthy right now. He's played at least 16 games in 5 of his 8 seasons including 2 of the last 3. He has 5 seasons where he has averaged over 20 ppr ppg. If he gets hurt, you can play someone else.
Scenario A: CMC gives you 10 healthy games and you have to use a bench player for the other 6 games.
CMC scores 22 ppg, your replacement gives you 11 (this is like RB 32 production). This gives you 286 points.
Scenario B: You wait for a steadier RB who gives you 16 ppg and stays healthy all year: 256 points.
Now of course the chances that Scenario B RB gets hurt and misses time is pretty good because that's life as a RB. It's also possible if you have CMC's handcuff or are a little craftier on the waiver wire that the replacement in scenario B is scoring more like 14 PPG. But from a simpe math perspective, I think if CMC plays 9-10 games you are getting a return on value even at pick 1. Those 286 points come out to 17.8 a game which would have been RB6 last year.
Not gonna pick apart your post line by line, but I largely disagree. Suffice to say there are way too many "Ifs" and using the ideal/rosiest view projections for me. But the reason his ADP is mid to late 1st round is because the majority of people agree with you not me haha. So from that angle, I get what you're saying.
My broader philosophy of fantasy is make the playoffs bc at that point it's largely a crapshoot who wins (IME). I don't NEED to hit on some uber high upside guy to do that like I would if I was playing in some 10k entry DFS tournament where it's impossible to win if you don't have Vick/LT/Faulk the years they exploded. What I can't afford to do is whiff on one of the first two picks I make. So in general, I avoid risk where I can there. To be fair to CMC, part of the equation for me has been mostly avoiding ALL RBs in the first round; so really the flag is already red for me, his injury history/bust potential just make it extra red hah.