I don't like or hate Mikasa, but she is talented. Deep down, I believe it's more to just saving Eren as you'll see later in the anime.(Unless you already read the manga.)To be honest I'd say it's the opposite.
Mikasa loses her focus more when he's in trouble than she shines. Look st what happened in the battle for trost.
She wrecked titans, but lost all of her gas.
She's easily the most naturally talented human fighter, but she lacks Rivaille's raw experience which makes him better for the meantime. Once she manages to lock down when Even is in trouble...she'll be far better off.
I believe Titan Killers are all naturally talented. When you think about, if you're not at the level to kill Titans, three things will happen:
1. You'll die.
2. Someone will die saving you.
3. Someone will save you.
Like Eren, he has experience, but he still suck.