Someone please explain to me what exactly you are 'winning' at when people scream "P2W!!!!"

Is there some kind of secret buff for having a shit load of items? Do you do more damage? Are you tankier? Is there a special move that lets you throw junk at enemies and nerf them?

So if I buy another retainer, I just apparently 'win' the game.... damnit SE, this is the worst secret ending yet!