I get what you mean, but in addition to that, I also think he's in the game and close to the MC for the as he balances out all the estrogen the MC is constantly around, while completely non-threatening as male when it comes to the girls, and he tries to use the MC's proximity to all the cute girls to his advantage. Hell, if I'm being honest, Miguel is more competition for the MC than Zach will ever hope to be.... in no way could Zach ever hope to compete head to head with the MC for whatever girl the MC wants....Zach is just hoping to get the scraps of whoever the MC doesn't pick.
That said, I also think Zach is also a version of other make protags we've seen in other games....the pathetic, horny, creeper/brother/son of whoever he's trying to have sex with. Which is why I now hate those games, as I can't stand when we're forced to play as a MC that thinks/talks/acts like Zach just because he's desperate to get laid.