It's probably much better than throwing a dart. Age progression and decline charts are real. Of course, several players bust out of the norm and have great beginning or ends to their careers, but most follow pretty close to the norm with a few blips here and there- possibly related to injuries.
This is one reason I felt it was very odd that 9 out of our top 10 returning players from 2016 saw declines in their OPS- some very significant ones. Only Vaz saw an uptick. Since most of our players were pre-prime or prime, and the others were not far beyond peak prime, I felt it was very strange. Yes, the loss of Papi and nagging injuries contributed to some declines, but I'm expecting upticks for a solid majority of our returning players this year.
2016 OPS> 2017 OPS (Listed in order or most PAs in 2016 (110+ PAs)/ Player & age
.897> .803 Betts 23
.802> .746 Bogey 23
.825> .760 Pedey 32
.835> .726 J.B.Jr 26
.866> .750 HRam 32
.705> .548 BHolt 28
.845> .644 SLeon 27
.850> .709 Young 32
.585> .735 Vazqz 25
.835> .776 ABeni 21
Amount of decline/ Player/ Age in 2017
201 Leon 28
157 Holt 29
141 Young 33
116 HRam 33
109 JBJ 27
94 Betts 24
65 Pedey 33
59 Beni 22
56 Bogey 24
+150 Vaz 26
Nobody was over 33 to start the 2017 season. All but Vaz declined.
Okay, throw out the top 3 and Vaz from this list for being reserve (platoon) players, but we still see 6 of 6 declines from players between 22 and 34, including 3 by 94 or more points!
All six declined by more than 55 points. It wasn't even close for our 6 best returning players. Add Moreland to the next list and possibly Vaz (if he increases his PAs this season) and we have 8 core players plus Devers (.819 in 2017).
I'm pretty certain we see upticks in 5 of those 8 players. I expect Vaz to decline and maybe Pedey. Certainly HRam and Moreland can do worse or the same, but I would bet on all 4 of these guys declining next year. (I actually think HRam will top .790 which is already 40 points higher than 2017.)
Of course, the odds are at least one from the other 5 declines, but I'm betting 5 or more improve their OPS. (I'm not counting Devers.)