Over time is isn't unreasonable to develop different disc preferences with your different throws. They're two different grips and motions. Needing varying disc to accommodate different throwing styles makes sense.
No it's not unreasonable, but also not strictly necessary. I myself have different OS/stable putters in my bag for grip reasons: Zone for FH and Rhyno/Serpent for BH. However, I'm also able to imagine a mold minimalist that throws a variety of Aviars--both FH and BH--to cover all of their putter slots.
It just bugs me for someone to say that the Philo bag isn't too simple for an all BH player, but it is too simple for a BH & FH player. It's purely hypothetical anyway, so why not imagine a FH/BH player that can throw those 5 molds FH as well as BH? I'd be interested to hear what additional mold(s) people think are needed to make a bag "complicated enough" for someone that throws a decent amount of FH shots.
(In reality, of course, Philo does very well throwing almost exclusively BH.)