I found this chart the other day while searching for something totally different and found it incredibly enlightening.
In terms of the top rushers from last year, only one back was near 90% of his team's carries. Gotta be AP, right? McCoy? Charles! Gotta be Charles... Nope. It was Forte.
- Charles took 62% of his team's rushes.
- McCoy took 79%.
- Lynch took 62%
- Ryan Mathews took 70% of his team's carries.
The redzone carries are even more interesting (Forte is the only one at ~90% there too), but I'll get into that later.
My takeaway from this, a workhorse isn't necessarily taking the vast majority of his team's carries. 60% was what guys who are considered workhorse status got. The dreaded timeshare backs (Gio/BJGE, Bush/Bell, etc.) were all in the 50% range.
Consume the stats at will.