So I am going to assume that you are referring to your Vikings team...
1) When choosing RBs, the most critical attribute is speed, far and away. Your top 2 RBs have speed in the 60s. 80 is about minimum to be effective, and 85+ is preferable. That is why there are some owners who use WRs in that spot.
2) Again, your top 2 RBs are in their 9th season, which is the first year of regression for that position. The first thing to go is speed. Both of your RBs have lost -4 in rating (by default weights, probably more using the ones I use), so I am assuming that they were probably both at least in the 70s for speed before, if not higher.
3) To me personally, the best running plays are out of 11 formations (1RB/1TE/3WR) and to the weak side. It's kind of a numbers thing, as well as that us when teams will run nickel defenses by default.
Hope this helps. There are a few other things as far as attributes for RBs that I look at. Acceleration, I forgot about acceleration. I prioritize that as well. But I don't want to spout off too much stuff that I don't know for sure is concrete. But any other questions, I would be happy to give my 2 cents.
