Now that I have more time, I'm going to elaborate on my earlier posts a bit.
Protagonists deal in two major currencies:
Power and Potential.
Is the character powerful enough to deal with whatever conflict he's facing, or does he have the potential to later defeat his conflict. I'll put examples from Dresden Files and Codex Alera:
Ye be warned, read all of Jim's books, up to the newest, or you may be spoiled.
SPOILER A-FREAKING-LERT!
Power: As it stands, it's clearly shown that Harry can set flame to an ancient manor, killing everything inside save for the extremely powerful. He can also blow enough wind to re-route a concentrated, pressure-driven stream of gasoline set ablaze. Harry also has the option to instill in himself necromantic energy of epic proportions, to allow himself to be taught by a fallen Denarian, and a powerful winter fairy, to submit himself as the powerful Knight of the Winter Court, and summon allies as powerful as a demonic mercenary and the Blackstaff of the Senior Council. Add on the fact that Harry already wields enough metaphysical muscle to burn down buildings at will. Or, additionally, Harry has the power to put it all behind him and lead a peaceful life with friends, a life that isn't wrought with danger and worry. Also a world with Susan.
But Harry doesn't wield either of those powers, because Harry has the guilt of the people of Chicago, the Special Investigation of the CPD, and the friends and allies, including the weak or magicless. Harry has the option to gain power, enough so to perhaps crush the earth itself on a whim. But Harry doesn't accept this power because of the effects of it. So, Harry, barely powerful enough, scrapes by through clever plans, magical tricks and trinkets, and determined allies. And his enemies aren't always all-powerful. It's the difference between a police officer and a criminal. The criminal doesn't draw the line as early as the cop, if he even draws the line at all. Harry has to draw the line. To not kill with magic, to not blow up the innocent bystanders locked in the closet. Harry's power is checked by his conscious.
Potential:
Tavi has potential, in spades. He's among the most obviously powerful strategists in Alera. He holds allies among the Marat, and perhaps the Canim (maybe.) He's now coming into fire furies (maybe?), and quite probably many more. But the reason he's lived to make such allies and surpass amazing expectations isn't because he had power, it's because of his potential. He was given tools which he used where others would or could not. He effectively did what many could not. He played to his strength well despite his weakness, and lived to the potential he needed to overcome his conflict, not once, but twice. Because of this, he makes a strong protagonist because of his potential, not his power.
End FREAKING Spoilers.
So, in summary, a protagonist can hold his own with or without power. If he's powerful, he needs something to keep him in check, if he has potential, he must come into his potential, or die trying.