I am sure. I don't think anyone expects him to repeat his 2016 season. Let's hack off 1/3 of his fantasy points from 2016 and it's still 14.5 standard ppg which would have made him RB5 last year.
So hacking off a third of his FF production is one thing, but you're assuming a linear reduction in stat categories across the board.
A straight .1 pt for 1 YFS and 6 points/TD puts Johnson at the following FF points accumulated for 2016 - 211.8 on yards 120 on TD's. 331.8 total. 36.1% of his point total was TD's.
One large factor Johnson was as prolific as he was in 2016 because he had 20 TD's. That's an outsized number to expect YoY if all conditions remained the same, much less changed the way they have in ARI. Is it possible this number alone could decrease down to 10? Let's recognize that 10 TD's in 2017 would have ranked 8th in the NFL.
On TD's alone, that would represent an 18% reduction in his 2016 point total
Now if he gave you 2100+ YFS and 10 TD's, you're still spiking the football...but how effective will ARI in moving the football? Bradford's health history is well-chronicled, Rosen starting game is a pure-wild card. Could he be Jared Goff rookie bad? I doubt it...but no one thought Jared Goff was going to be THAT bad heading into 2016. And while Jared Goff wasn't the only reason LAR imploded that season (***cough*** Jeff Fisher)...the accumulation of external negative circumstance contributed to Todd Gurley, the same Todd Gurley who is seemingly a consensus 1.01 pick this year - to plod toward a 1212/6 season. Noone was satisfied with his 'floor' that year.
Now - I'm not predicting DJ regresses or performs to this level whatsoever. But what I am saying is that there are enough negative circumstances surrounding this franchise at the moment to produce a catastrophic season all-around. QB may look good for the long term, but there could be (likely be) some growing pains here. The coaching hires following Arians departure have been seen/viewed as quite underwhelming. The WR's behind Fitzgerald include Brice Butler as the #2 WR and Christian Kirk (a guy I like, but still a rookie learning the pro game with a transitory QB situation).
I know I'm a broken record, but the key to Round 1 for me is always avoiding the land mine that you didn't see coming. It's not the player I'm concerned about, but the situation for at least this season feels unsettled at best, and one that could derail Johnson through no fault of his own.