Go ahead, then divide by all the RBs drafted and tell me what the percentage is. Spoiler: it's extremely low, which is my point. Picking individual data points does not change the probability of being drafted in the first round vs all drafted runningbacks.
Your argument = some great RBs in the first round, ok fair.
My argument = some great RBs in the first round ÷ all running backs in all rounds.
My number is much smaller. That's what sets the typical price for RBs, not the outliers at the top.