My opinions are not based solely on these numbers. I watch every pitch of every Sox game, and I play extra close attention to SS defense. I saw a clear decline in Bogey's defense from 2015 to 2016. He was not bad, but he was not good either. He was far from "very good", in my opinion in 2016.
IMO, Bogey's defense ranges from fair to decent at best. If someone said he as just "good", I'd be okay with that. "Very good" should mean at least top 6 or 8.
Maybe we just view these terms differently, and we are just arguing semantics. I tend to use comparative analysis when using superlatives. Bogey's certainly a much better fielder than almost everyone on the planet, but when compared to the top 30 MLB SSs, he's probably ranked about 13th to 20th on SS defense from what I've observed combined with the data I value. If someone wants to call him 10th to 12th, I would ask them if the truly think he's better than which of these guys:
2014-2016 UZR/150
20.2 Lindor
19.8 Simmons
15.6 Russell
13.5 Hardy
12.7 Cozart
11.7 Crawford
(To me, there's no way anyone can say he is top 6)
7.9 Seager
7.9 Iggy
6.3 Galvis
5.4 Hechavarria
5.0 Tulo
(I cant's see a reasonable argument to say Bogey is to 10 or 11.)
From here down, it's a close call:
2.8 A Escobar
1.7 Peralta
0.5 Gregorius (surprising low number here)
0.1 Lowrie (surprisingly better than I'd have imagined)
0.0 W Flores
-0.1 D Espinosa
-0.8 E Escobar
-1.3 A Amarista
-1.4 Castro
-1.6 Bogey