I haven't checked Grace, but notice with Diekman, his fastball % exactly matches his "sinker" %:
https://www.fangraphs.com/statss.asp...003&position=P
Which means to me he throws only 2 seamers, and his get sink. Not all do:
https://blogs.fangraphs.com/players-...he-same-pitch/
Corbin however doesn't have the same % of fastball to sinkers - he clearly also throws fastballs that don't sink, so either he uses some 4 seamers, or he throws the 2-seamer with slightly different grips:
https://www.fangraphs.com/statss.asp...323&position=P
So where is his 4 seamer in OOTP/PT? PT has been around for 2 years, he's thrown fastballs that don't sink about 20% of the time in those 2 years.