It doesn't matter who's on the Avengers, it just matters that you don't have 3 of the same power level (unless it's retardedly awesome power level) or a couple redundant characters.
Luke Cage's strength level has never been documented. Even if he is at level 70, Iron Man and Sentry are stronger and more durable than he is.
Cap, a great tactical leader and fighter, but nothing really super.
Spider-Man, I like Spidey on the Avengers. You looked mainly at his strength, when he's much more than that. He's a mid-level super guy all around. Strength, amazing agility, preconitive senses, wall crawling (good for espionage missions) and his webbing. He also has brains, and would make an interesting addition to any Avengers team (and he was previously a reservist).
Spider-Woman, a bit redundant here, sure she can fly--since Bendis follows the 60's cartoons more closely than the comics, and has electrical powers, but nothing really helpful, nor anything that makes her one of "Earths Mightiest Heroes"
Ninja dude, it's Matt Murdock. He has super senses and fights well. Nothing really outstanding here.
Wolverine: enough already.
Sentry: finally someone who's actually mighty.
Iron Man: A good level of might, plus skillz and money.
Here's what "Earths Mightiest Heroes" should look like.
Mike Patton.
But seriously: Iron Man, Sentry, Thor, Dr. Strange, Silver Surfer, Namor, Captain Marvel, Black Bolt, Moon Dragon, Photon, Binary and Captain America (because someone has to do the cleaning around the clubhouse)