Analytics would say don’t send a starter through a lineup a third time, which probably has something to do with why the starters get pulled early. As @Frobbypointed out, that’s pretty standard league wide, and doesn’t really explain the bullpen usage.
I sort of doubt it’s sig/data driven either, given that the other analytics heavy organizations don’t do it. Otoh if they didn’t like it you’d think they’d have a conversation with him.
Regardless of who is to blame, this is my single biggest long term worry with this team right now.