he isnt really,
most of the jounins from clans are stronger.
If Jiyaira did missions for the leaf he'd be considered a jounin so he'd the strongest, Orochimaru was the strongest jounin at the time that he was in the leaf.
Kakashi hasnt got a reputation the size of theirs, hes good but hes an average jounin when you compare him to some of the strongest

Hyugas leader isnt really a jounin either though - he doesnt wear a head protector and let Hinata train with Kunerai only after he had rejected her, this suggests that the main family train all their members and therefore they dont have the ranks such as genin jounin etc, they're only equivilent.