David Boston had 473 yards and 2 TDs his rookie year.
Larry Fitzgerald had 780 yards and 8 TDs his rookie year.
Michael Floyd had 562 yards and 2 TDs his rookie year.
Even the mighty Anquan who had 1377 yards and 8 TDs his rookie year came back down to earth with only 600 yards in 2004 during Fitzgerald's rookie year.
As a rookie, Marvin Harrison Sr had 836 yards and 8 TDs for the Colts in 1996, his rookie year.
MHJ has 726 yards and 7 TDs so far this year, with clearly elite games against Miami and the Rams, while in most games he's looked fairly mid.
Bottom line - yes he looks soft at times, yes he drops catchable balls, and yes his routes are soft. It takes 3 years to develop a competent elite WR not named Jamar Chase, Calvin Johnson, or Larry Fitzgerald. Give him time, teach him when the ball is in the air that it's his and he needs to rip it out of the sky destroying anyone in his path, and he'll be fine.
If he can't do that, we will eternally compare him to DeAndre Ayton, but I think with time he'll be fine.