The only reasonable complaint in here is "my ex's new wife is calling me about minor things because it's easier for her than calling her husband/the child's father."

That's from the angle that this guy is dumping all the emotional labor on the women. Either everyone is taking this for granted, or the man is pushing back hard when asked to do his share: his current wife apparently prefers to call or text LW than either consult Guy on the small things or point out that "this is your daughter, and the LW is your ex, not mine, it's not my job to talk to her."

However, given the rest of this letter, I suspect that if Stepmother did start calling her husband/the girl's father instead of bothering LW, LW would complain further about being pushed out. Because this complaint doesn't even make sense: if the ex was somehow trying to replace LW's daughter with a dog, it would be easier for LW to compete with him for their child's attention.