WTH! In the contrary, it's because he didn't control Shukaku at all that he couldn't even sleep calmly.xd That's the reason why his father even wanted to kill him. Just because he couldn't control Shukaku and that when Shukaku could emerge from his body and could be dangerous for the village. Shukaku, who is even the weakest from all Bijuus. If he slept, the Shukaku could be outside easily.
And yes he beat 2Kages but in which conditions? His father went on his own. Against Mizukage? Mizukage helped him several times to defeat him and he was not even alone. He had a team on his side only against one man. He told him that he was in a genjutsu. If it was a real fight and that Mizukage didn't tell him before, Gaara would not even try to get through it. Even during the genjutsu, Mizukage never tried once to kill them when he could. Tsuchikage is the one who destroyed the claim. And a sensor is the one who helped Gaara to know where the real Mizukage was during the jockey boy. I acknowlege Gaara is strong, but he never defeated someone on his own since Lee in part1.
Kakashi defeated Zabuza and Haku, Kisames master and probably other swordsmen(but we don't know about it, so i leave it like that), fighting against several Bijuus where he even thought he could kamui 5/6Bijuu balls, and fighting along with Naruto, Gai and Bee the final boss of this manga.