Hey, bro. Sis, whatever. Remember this is a new game. AKA, there'll newcomers. AKA, "your" character could debut in the newest game. Just saying... .... Anyway, what I mean to say is that each new installment can easily bring a character whose characteristics may tickle your fancy, maybe to the point of wanting to main him. And even if you don't quite find a character that suits your style, whoever fits the closest may be enough for you. It's, you know, getting used to it. In the corniest way possible to say it, "you'll have to wait until the one you want show up".
Now back to the Miis themselves, if customization ISN'T their gimmick, then what will? Hammerspace? Great, always nice to know you can play as the bland, boring, non-charismatic version of Mr Game and Watch/Villager. Really, if Miis aren't in for the sake of being custom, which is, you know,
the whole purpose of their entire existence, then what the hell were they in for?
And it may be my opinion, but you've gotta admit that it's a pretty absurd design choice to create several multiple unique characters and then have on that can be customizable to any possible degree, therefore rendering everyone else obsolete. Who wants to play as Mario, Sonic, Link, Kirby or any of those suckers when you can play as freaking Mecha Jesus, who uses an lightsaber cross as a boomerang?
Okay, maybe that's a bit too exaggerated, but my point stands. If you aren't conformed with the diverse plethora of characters, each one having their own vibe and play style to them, that they offer you thorough the entire series, even though there's still the possibility of getting your most desired character in the next game, then sorry, but you're playing the wrong game.