That's kind of the point. He was best suited for the position and is probably the most talented, humble, peaceful minded ninja that was available, but he had to give everything up to do what he thought was right.
Speaking of what he did, he had to be really, really strong to take out the entire Uchiha clan. I know we don't know much about them, but his dad is at least insinuated to be a pretty competent ninja, and there were probably a good amount of jounins at Asuma or Kakashi's level. I know Madara can summon meteors and Hashirama can summon wood dragons and giant gates and that they can even alter the landscape with their awesomeness, but I think Itachi had to be at least approaching their level. He was also a good deal younger than both of them at their prime.
We really never get to see the extent of Itachi's power. He's terminally ill during Shippuden, possibly even during part 1.
Edo Itachi curbstomps sage Kabuto. Itachi is probably around Nagato's level (and Nagato really was much more powerful than sage mode Naruto, it's just that he had been fighting the entire leaf village, had to deal with the fury of naruto using the full power of the 9 tails, and was also diluting his chakra into 5 separate bodies.).