Persona 3 was remade into Persona 3 Portable where you could pick a female main character instead of a male, and P3P is widely regarded as one of the best games ever made. Persona 2: Eternal Punishment featured Maya as the main character after she was the primary focus of Persona 2: Innocent Sin. P2 as a whole is widely regarded as one of the best stories ever made. Persona 1 didn't really have a main character in the same sense as 3, 4, or 5 do, and was popular enough to spawn the rest of the franchise when it itself was just a spin-off of the SMT series.

Nothing about Personas 3 or 4 prevented them from staring a female MC from the get go or having both options available. With Persona 5, for the full effect of the origin story of the MC, a slight change probably would've been sufficient if they wanted to have the MC be female or make the MC have either gender.

As for target demographic, that seems pretty unlikely. Plushies aren't generally viewed as a big thing among young men, and are one of the main pieces of merchandise that is popular with the series. P4: Dancing All Night featured a female MC and was all about dancing, and I don't think that would've been made if the target demographic for P4 was just young men.