More yards, first downs and touchdowns are the result of opportunities, not ability -- Julius had the same average per carry as Thomas, and he had a much higher average per catch. Thomas had 21 of his first downs on third or fourth down; Julius had only three carries all season on third or fourth down (and converted on all three). On first and second downs, Julius had a higher YPC, more first downs and a higher first-down percentage.
And it doesn't take "home run" ability to run for 20 yards. Thomas' longest run all season was 30 yards, and he scored only one touchdown longer than 7 yards. Julius had three runs longer than Thomas' longest, including a 77-yarder, and only one of his touchdown runs was shorter than 14 yards. And we hardly used Julius as a receiver, but he had three catches longer than Thomas' longest catch.
In the playoffs, against the same defense, Thomas rushed 21 times for 66 yards, with a long run of 9 yards. Julius rushed 22 times for 112, including a 35-yarder.
There's no way I'd take Thomas over Julius.