Quite the opposite.
P is two fare classes above G in domestic first.
Z is the lowest fare class in int'l biz, with the the hierarchy being JCDIZ.
T is third from the bottom on coach, not counting basic economy (YBMSHQKLUTXVE).
So I'm curious to see what the required booking class is for int'l biz, and what the previous booking class was for coach.
But at least for domestic first, being able to use SB certs on P fares instead of just G is actually a very big positive.
Where did this information come from?