I think he is the youngest Kage. And, to be honest, probably the weakest.
Yes, Tsunade could beat him. Remember, she is one of the Sannin. Why it may be just a title, it speaks for itself. Her strength is more than enough to **** up Gaara's shield of sand and sand armor.
On top of that, Gaara being Kazekage isn't quite as impressive as Naruto becoming Hokage. Unfortunately, Sunagakure doesn't have too many impressive ninja as only Baki, Gaara, Kankuro, and Temari stand out. Baki's only shown skills typical of an average Jonin.
Konoha, on the other hand has Kakashi, Tsunade, had Jiraiya during the actual manga timeline, Danzo, Neji, Hinata, Gai, Asuma, Kurenai, Sasuke (until his obvious defection, at which point even before, he stood out), Hiashi Hyuuga (or Hizashi, can't remember which), the Hyuuga clan in general, and even little Konohamaru.