The JBJ scores are puzzling, but I will say, he doesn't look as good as he was a few years ago. IMO, he is not a minus, but there are a hell of a lot of great defensive CF'ers in MLB these days, and these numbers are somewhat relative to the norm.
JBJ's numbers look wrong to me, and it seems strange that over the last few years, he starts off in the negative and ends up plus. Maybe he will again this year.
I've never said the numbers are perfect or 100% accurate. Park dimensions and the ability and speed of corner OF'er affect a CF'er's ratings, as well, and that doesn't seem fair, but these guys watch every play of every game. They are calibrated, cross-compared and rotated, so one would think that over a large enough sample size, it would be fairly accurate. OF'er sample sizes can be pretty small, and maybe a 2-3 year sample size is the best way to use UZR/150 on them.