It's closer than you think. Numbers aren't everything, but:
Shenault: 8.4 catches per game, 112.3 ypg, 11.8 ypc, 11 total touchdowns. 115 rushing yards, 6.8 ypc.
Moore: 8.8 catches per game, 96.8 ypg, 11.0 ypc, 14 total touchdowns. 213 rushing yards, 10.9 ypc.
Shenault played 9 games and Moore played 13 which is most of the difference in their numbers. If they played the same number of games, Moore only wins in catches (barely) and yards per carry (significantly) - but neither ran the ball very often. Moore adds returns as well, but honestly he was not a good returner last year. 20.1 yards per kick return and 6.8 per punt return, no touchdowns. Moore is absolutely a more exciting player to watch, has more highlight-reel plays, and gets bonus points for playing B1G defenses instead of Pac-12, but there are arguments for Shenault here.