Two months ago, Lukas Berger confirmed that pitcher's velocity decline without injury in the mid-20s was not intended, then velocity decline was reduced in the last update. But it's still common to see atypical declines. The picture below is the result of simulation with injury turned off.
As far as I know, it is not that common for big league pitcher to lose more than two miles of velocity before age 27. However, when I tested standard league with injuries off, pitchers with 97+ mph losed more than 2 miles very frequently.
I compared the maximum average velocity to average velocity at age 27 of pitches thrown more than 100 innings in a season in the last 10 years and checked how many players had lose their velocity by more than two miles, then did the same thing in the OOTP standard league with injury setting off. In OOTP, 16 pitchers with 97+mph lose their velocity by more than 2 miles while 4 pitcher had little change in velocity. On the other hand, there's no big problem with pitchers under 96 mph.
In summary, the problem is that young pitchers with 97 miles or more have a big reduction in their velocity even though they are not injured. This is strange compared to the big league over the last decade. While this won't have a very significant impact on gameplay, it's not pleasant to see a pitcher go through what he has to go through in his late 20s a few years early.
Just because I've compared OOTP to MLB it doesn't mean I'm arguing that OOTP should be made the same as reality. But If a series of patches that have been done to increase the reality of the game have made the game more distant from reality, this is a problem and should be fixed. I think the game shouldn't be harsher or more extreme than reality at least.