He wasn't defeated by anyone...are u talking about the guy who was killed by a chunnin?
Based on this logic Obito is defeated by a genin.
and soon kaguya aswell.
Not to mention he didn't die because of Gaara. Gaara himself admitted inferiority.
And Kimmimaro was going to kill Gaara till the disease kicked in...obito wasn't defeated by a genin ..
he was defeated by naruto , sasuke, shikamaru, lee, choji, ino , tenten, kiba, shino, hinata, sakura, ... and 2 hokage level ...minato , tobirama ,,, with a little assist of 2other hokage level ,, and +50k SA shinobis .
And Kimmimaro was going to kill Gaara till the disease kicked in...