It is hard to compare players based on a set number of carries because you have to consider the circumstances. For example, Elliott had 304 carries last year, which means not only did he touch the ball quite a bit more than Henry (215) but also that he was a focal point of the offense. How much of a factor that played in their relative success is hard to determine, but it can't be disregarded.
We have no idea whether Henry would have sunk or swam here given the same demands. His first year he only started two games and carried the ball 110 times, compared to 322 by Elliott. The next year, Henry again started two games (played in 16) and had 176 carries to Elliott's 242 (playing in 10 games). Would Henry have been capable those first two years of being the kind of workhorse Elliott has been?
Right now, 2018 was a career year (outlier) for Henry. So far this year, he's averaging 4.1 per carry while Elliott is averaging 4.6. Up to this point, Elliott has averaged at least 4.6 in three of his four years. Henry has only averaged 4.6 or better once in four years.