thing is, the answer is already given in the manga/anime. why else is the Uchiha clan known as the number one clan in Konoha? The Hyuuga are only the number one clan now because the Uchiha got slaughtered by one man... an Uchiha himself...

Shi_No_Shikaku: the sharingan doesnt drain very fast... only on non Uchiha clan members...