Well, if Betts falls somewhere between 2015 and 2017, or better yet, 2015 and 2016, he'll improve.
Same with Bogey and JBJ. I agree, projecting JBJ is a tough one, him being so streaky and all. Yes, projecting Beni is hard at such an early age. He may still have adjusting and counter adjusting to do, before reaching his stride.
In totality, I expect these guys to improve on their 2017 numbers, but I'll also not be at all surprised if they improve on their 2016 aggregate numbers as well.