(My point of view, in seeing Leo as a boy, is that I saw his shoulder-to-hip ratio, I didn't see any curves, the voice sounded boyish to me, I"m sure you get the idea. And after I did some digging, I saw the lack of consistency firsthand.)
"shoulder-to-hip" Ya know that Leo's shoulders is just covered if you will look in T6 customization?
"the voice sounded boyish to me" For you. But you don't know who is German voice actor/actress, maybe it's an voice actress like Veronica Taylor.
"And after I did some digging, I saw the lack of consistency firsthand" I did it too, but diffrence between us that you want to believe that Leo is a boy. I also believed that, until i saw many things that does not look like it belongs to male at all. For example. Will male wear female haircut? Will male wear choker that can only female do? Will male wear a tiara or cat's ears accessories? No males in Tekken doing it besides Leo and any other females.
Look, we can argue about this alot, but let's agree about 1 thing, that both of us sees Leo as it is.