the Juubi is NOT COMPLETE, has anyone thought about that? It doesn't have it's original form because the two MOST potent parts are not there.
As we seen in the flash back it had a body that was shaped similar to Kurama, remember?
I mean if you think about it for a minute before we insult it, it makes sense. If you leave out the most important ingredients BUT substitute fractions of them this is what you get. Also a summons doesn't have to be a creature. Tenten summons her weapons all the time.
Sasuke summons his shuriken form his wrist as well.