Yes, I had studied the earning scheme for XP and miles which is why I think I should have earned 12 XP total (instead of 4) and 175% mileage bonus (instead of 150%). I'm awaiting an email response from FB.

FB's earning scheme for its Delta partner on the FB website (to which you linked) has not been updated to reflect Delta's domestic booking class realignment. The realignment changes domestic first class fares from F, P, A, G and R to J, C, D, I, Z and O.
https://pro.delta.com/content/agency...rkets----.html

So a Delta domestic flight should earn either 2, 4, 6, or 10 XP, depending on booking class (Economy, PE, Business, First, in your 1st link). It won't earn 10 XP because Delta First Class (old FPAGR, now JCDIZO) is considered Business Class as noted on FB's partner page for Delta (in your 2nd link).

I flew two domestic segments in J (previously F before realignment), which according to the earning scheme in the links you provided should earn 12 XP total and 175% mileage bonus UNLESS there's still something I don't understand (which is why I started this thread to ask) or FB changed its rules and hasn't updated its website after Delta's booking class realignment.