I’m just going to leave this dev chat Q&A here which gives the answer
Does pitching fatigue now use total pitches per season at all? I have noticed that starting pitchers every time they get to 100% leads to bad performance as if there were being overused. And that this gets better if the pitchers are rested. Are all 100%s not equal? Is there is hidden factor? Total pitches, starts, or anything else? (baldric - Hall of Famer - 1:07 PM)
No, there is no such thing as "total pitches per season" in HBD like there is in SLB. In HBD, a pitch tank system is used. The depth of the tank is based on their stamina/durability ratings. It's adjusted based on usage. All 100% are handled the same, nothing hidden under that number.