The Pats did the same thing drafting Michel in the 1st, but ultimately team philosophy wins out and they didn't use Michel like a workhorse, they integrated White and Burkhead disregarding draft capital. Now they have Harris, who could beat out Michel, but still will be in some kind of rotation. The Eagles have shown no indication they like using a workhorse. They traded for Ajayi then used him sparingly. They use their backs like the Pats and I don't see that changing.
Is that a function of team philosophy or personnel? Do you really think the Eagles and Pats would rigidly stick to a RBBC if they had Saquon Barkley or Joe Mixon on their roster? There's an old Bill Parcells quote where he says something like, "If you have two quarterbacks, you really have no quarterbacks." Likewise, there's a good argument that RBBC only prevails when teams have no one worthy of being a bell cow back, and not because the team
wants a committee.
Go down a list of the elite backs of the past 10-15 years and you won't find them sharing a lot of work. Once they showed what they could do, people like Forte, Rice, McCoy, Charles, S Jackson, Peterson, Lynch, Zeke, Bell, MJD, LT, and Gurley were fed the ball. The Patriots haven't had a back of this caliber since Corey Dillon, so it makes sense that they've relied on a committee approach. LeSean McCoy and Brian Westbrook handled a lot of work when they played in Philly. The Eagles haven't had an elite back since trading McCoy, so of course they've used a revolving door. What else would they have done? Feed Smallwood 300 touches?
I just think you are making excuses to favor Montgomery over Sanders when what you're really saying is that you just don't think Sanders is anything special. That's fine, but let's not pretend that the situation itself is some kind of permanent RBBC lock based on recent history. If last year's Eagles team had a prime Westbrook or McCoy on the roster then I'm guessing they would've fed him 250-300 touches. That's what you do when you find a back that good. When you have a bunch of garbage, you fall back on a committee approach. So what I'm saying is that IF you think Sanders has a chance to approach the level of McCoy/Westbrook, the presence of scrubs like Adams and Smallwood is absolutely irrelevant.
Put another way, you can look at the population of the NFL's RBs as a tiered pyramid.
GROUP A - Elite backs who will start for any team and have virtually no vulnerability to draft picks/free agent signings (Ex: Peterson, SJax, LT, Barkley).
GROUP B - Good backs who can be effective starters, but aren't elite options (Ex: Benson, L Miller, D Murray).
GROUP C - Backs who have enough talent to thrive in spurts, but are extremely vulnerable to being replaced by better talent (Ex: Z Stacy, J Howard, CJ Anderson).
GROUP D - JAGs who are eminently replaceable and only have value in the event of injuries.
Part of what I'm arguing is that when it comes to dynasty value where you're looking at performance over a player's entire career, your #1 priority should be trying to identify which bucket the player belongs in because that's ultimately going to be the biggest variable in his long-term success. Would I say Miles Sanders is a Group A guy? No, that would be a very dangerous assumption, but it's possible and if it turns out that he's even just a Group B guy and Montgomery is a Group C guy then you will regret passing on him just because the depth chart looks bad (and it's really not that bad, as nobody on Philly's roster has a good case for being more than a B, and are probably closer to C).
Personally, I'd have Sanders shaded towards Group B and Montgomery shaded more towards Group C. Maybe I have it backwards, but what we know from decades of data is that good talent creates opportunities whereas bad talent wastes opportunities. The Rams are a good example of this. They spent a 5th rounder on Zac Stacy and at the time he was the best back on the roster. He had a productive rookie year. Then they drafted Tre Mason in the third round and he stole a lot of Stacy's thunder. Then they drafted Gurley in the top 10 and all of those guys became irrelevant. If Montgomery or Sanders is just pretty good then nothing will stop their team from dipping back into the draft and supplanting them. It happens all the time. People took Bishop Sankey and Montee Ball with top 5 rookie picks because of their "great opportunity" and now both guys are out of the league. If Montgomery comes in and average 3.6 YPC as a rookie and the Bears are staring a franchise back in the face next year in the first round of the draft, are they really going to pass on that guy because they have David Montgomery?
At this point I'm repeating myself, but if you are worried about the likes of Josh Adams and Wendell Smallwood then you are maybe focusing on the wrong variable. The more talented a player is, the less it matters who else is on his roster. We can't assume either of these rookies is a Peterson or SJax who will have bulletproof job security, but their workload and long-term job security will mostly hinge on how good they are, and not much else. If you are really worried about people like Smallwood and Adams keeping Sanders off the field then to me that just translates to, "I don't think Sanders is very good."