Tony Dorsett: 5'11", 192 lbs
Emmitt Smith: 5'9", 216 lbs
Walter Payton: 5'10", 200 lbs
Barry Sanders: 5'8", 200 lbs
Compared to some of the NFL All Time best rushing leaders, Tony Dorsett definitely was not small.
Tony Pollard: 6'0", 209 lbs
Tony Pollard is about the same size, and he just rushed for 1k+ yards as a part timer as you mentioned. Even if used as a part timer, Tony Dorsett easily could have rushed for 1k+ yards every season in today's NFL and not have to be worn down like Zeke was. I would take Tony Dorsett today over any current part time RB and most full timers.