As a Vikings fan, it would be tough for me to pass up Jefferson at 10. Then I’d wonder what to do with my next pick.
Jefferson paired with Adams/Diggs and then just pepper mid round and late round RBs could pay off.
Jefferson's ADP isn't as late as 10 in almost any format. In PPR he is going 5th to 6th overall, and in standard like the discussion we are having above, he goes 6th-8th at the latest. So yes, if he's there at 10 that should be an automatic pick.
Jefferson's ADP is 6-8th (looking at FBGs page CBS has it at 18 for some reason) but that isn't the latest he is being drafted. As you pointed out ADP is an aggregate of thousands of drafts, if his average is 6, 7 or 8 that means he's being drafted both earlier and later than either of those positions with some regularity. We would need to see the range behind the ADP to have a better understanding of potential outcomes.
I only found two sites that include ranges of draft position but, for example,
Fantasy Calculator has his high as 1.01 and his low of 2.01, on
MFL (recent 12 team redrafts, real drafts only) he's going anywhere from pick 6 to pick 19 with an average of pick 10. For According to MFL Kamara it's 10 to 34 with an average of pick 19 and Barkley is going anywhere from pick 9 to pick 58 with an average of pick 23. It's about the same for Fantasy Calculator.
It is reasonable to think Jefferson could be available at pick 10. It is also possible that both Kamara and Barkley will be gone by
@VikingFrog 's 2nd pick.
You can't look at highs and lows, as there is always outliers. Some dude could be Jeffersons cousin and take him at 1.01. The average draft position is the best and most accurate data there is.
Is it reasonable to think Jefferson COULD be available at pick 10? He COULD be, but on average he is NOT. Which means he is more likely NOT to be there, than he is to be there. Same with Chase. Same with Kupp. So the most LIKELY scenario is that 6 RB's are taken by pick 10. You said anywhere from 7-9 RB's would be gone in the first 9 picks... and that would be considered unusual.
As for Kamara and Barkley, I mean you said it for yourself. They are going on average at 19 and 23... is it POSSIBLE they are BOTH are gone by pick 15? Sure, anything is possible. But it is HIGHLY unlikely, and maybe 1 in 100 leagues would have them both going top 14 when they have ADP's of 19 and 23.
You also asked "What would you project the 1-9 picks to be if both Kamara & Barkley would be there at 10?" as if you doubted they'd both be there at 10. Both will be there at 10 in the vast majority of leagues. Based on their ADP's, both Kamara and Barkley are there at pick 10 in 99% of leagues in this format, so I don't get your doubt there.
When we draft, we are looking for value. Why would anyone take Kamara or Barkley at 10 when there's a 99% chance of them being there at pick 14?
EDT: For the record, I'm big fans of Barkley and Kamara this year, but they're not even close to consideration for me at pick 10. I'd take one of the 3 WR's if they somehow slipped to me, or else a guy like Mixon, Chubb, or Cook, and then grab Kamara or Barkley (take your pick) at 14.