Thats part of it, but there are a lot of factors at play. One of which is the change in abilities between JT and Cardale with the read option. Second, they were breaking in a new oline without an established back early in the year - Zeke didn't lead the team in carries until the 4th week, and then 2 subsequent games he had less than 12 carries. As Ross pointed out during the season, Zeke also was running with a forward lean to generate power that somewhat stripped him of his big play ability (how many times did he look to be one step from breaking it but fall forward). I think the turning point was definitely the MSU game, when he started running more upright and broke off some runs.
Look at what he did starting with Sparty:
11/8 @Michigan State 23 car 154 yds 6.7 avg 2 td
11/15 @Minnesota 18 car 91 yds 5.1 avg 0 td
11/22 Indiana 13 car 107 yds 8.2 avg 1 td
11/29 Michigan 17 car 121 yds 7.1 avg 2td
At the same time, Barrett was carrying the ball 14, 17, 20 and 15 times.
Minnesota was the outlier over the last 7 games where he didn't lead the team in rushing (JT had a fantastic day with 17 carries for 189 yards and 200 passing; 4 total tds).
I think with more carries, he would have had world-beater numbers in those games. That being said, the workload that JT took on definitely kept Zeke in better shape for the run at the end of the season.