I don't think anyone truly into advanced metrics looks at Johnson's BABIP and says that he shoudl suck. Lots of other factors are involved. i'm pretty sure everyone who's said that Johnson will eventually come down (and he will, whether it's this year or next or the one after that) is saying that he will because he's performing at an impossible level.
Since 1945, only 4 players have had a season with a BABIP over .400. Roberto Clemente, Manny Ramirez, Jose Hernandez, and Rod Carew. Carew finished with a .408 as the high man. If you think Johnson is a better hitter than Rod Carew well then have I got the Bridge for you. Sarcastic comments aside, since the end of WWII the highest BABIP of anyone with a serious sample are Rod Carew and Derek Jeter who have a career average of .359 and .354. And Johnson is not way better than either of those 2 to say he'll be a .400 BABIP guy his whole career.
We're not talking about say Freeman, who has a high BABIP of .365. That's not out of the question that he can hang near that level, especially since his LD% is right around Chris Johnson's and he has a lower IFFB% (aka balls that are almost guaranteed outs)
BABIP is highly misunderstood because it's not something you can just look at. I forget who I had a discussion with this about before when he said Gattis was unlucky because of his BABIP and I pointed out his low LD%, high FB% and lack of speed don't lend themselves to a high BABIP and he's probably not far from where he should be.