I thought I’d come back & add (for anyone reading these at a later date), I went back and added in seasons with just an average of 12.5 att/game (200/16 games), min 10 games (for all years 1970-2016), and pre-90’s was actually similar to post 00’s. I looked at 250 & 275 (/their per game equivalents) and it held true — 275+ it really stood out, 1994-2007 was the peak of “high carry runners” (regardless of % of team yards), while the remaining years bounced around in the same range. (ie: The concentration may be higher now than pre-90s, but the overall rates of high-carries are roughly the same).

I’d say the conclusion stays the same though, that whatever level of RBBC you want to label the modern rushing-era with, it’s no different than before the 94-07 boom in workhorse backs. I imagine there was a boom partially because more-modern eras tend to have better scouting & finding the super-talented backs who can handle being a workhorse, but it did not continue because the increase in passing led to teams giving more time to backs who can handle complicated passing concepts. (That there are so many passes, it’s not worth it to keep in the potential workhorse if he’s not also a good receiver).