I don't think that's the case. IOW, a 100 doesn't become a 92. I don't play my guys into the low 90s so I don't have any real data. But I've played against teams that are all 92% and they still win games. The only thing I've really noticed, and it's in the minors(because I don't play fatigued BL players), is an increase in injuries. It seems that most of my minor league position injuries at 97% or less. I'm sure there's some small performance penalty for fatigued players but I don't think it's big.
That said, I don't think we can say MLB players play 150+ games with no change in performance. That's just something that can't be measured.