Totally with your train of thought. Most or every analyst that predicts stat lines, especially in the offseason, will project average performances that neatly line up to the stat lines guys will end up with. But there are always ebbs and flows.
I think with your cons though, you chose three bad examples to criticize guys on. Kamara, Juju, & Tyreek were three of the most efficient players in 2017. I don’t think you can fault people for not expecting the same efficiency the next season just because it rarely happens. (Unless you’re talking about special special players which the 3 of them are)
Kamara - finished as the #3 overall RB as a rookie in '17, 80% of his games he was either an RB1 or RB2. The guy scored 13 TDs on 200 touches. He averaged 7.7 yards per touch… as a rookie. (For reference when DJ had his 2,000 yard season in '16 he averaged 5.7 ypt).
JuJu - finished as the WR22 overall in 14 games as a rookie in '17. He basically did that from week 8 on (when he had that huge game on SNF against Detroit). He only had 58 receptions. IIRC, Jason was actually really high on him coming into '18 but you’re right Andy/Mike were both iffy on if he could repeat that efficiency to be a top end WR.
Tyreek - another one you couldn’t really predict finishing were he did last year just because of how boom or bust he was in '17. This was the year where he basically went off on odd weeks & was super down on even weeks - and still finished as the WR8. Now he’s a little harder to argue on being efficient because of how up & down he was, but it’s really that he made the most of the touches he did have. Granted, they can (& probably should’ve) recognize that he’s an absolute freak athlete who no one could cover. But, in my opinion at least, you can see how some wouldn’t be all in on him he the WR#1 overall last season; adding in that KC was introducing a young/unproven (at the time) starting QB).