Tobi's S/T simply made him a factor, but not worth ranking as he didnt demonstrate anything except avoiding attacks. His true power came once obtaining rinnegan and whether he used any of its ability is besides the point since we know what he can do with it. Having bijuu was enough and Gezo is enough at this point.
speed, immortal, fast defenses and skill level does matter and we've seen how the skill differs from how Itachi used it compared to Sasuke.
What true power, he has shown nothing with the rinnegan, he is just using that same old S/T. He has used the outer path once. thats it. No other rinnegan power.
He is even controlling the bijuu with his sharingan, All the rinnegan is there for it a fail safe incase one breaks his sharingan Genjutsu. Nothing more.
Obito's S/T is the only reason he is causing Naruto/Kakashi/Gai so much trouble, his rinnegan has nothing to do with it.
Obito wen't from being a mid skilled chunin, To being able to completely slaughter a hidden mist shinobi squad with no Training or anything (since he had only just gotten out of bed, A little help from zetsu also).
Fact, Obito's S/T (Pre-Bijuu/Pre-gedo mazo) was the only thing keeping him kage level.
The only shinobi that can defend against amaterasu are Kage level, Out of the current kages, only the raikage can defend against amaterasu.
The Sasuke vs Bee fight was prime example.
Bee was in another league to the sasuke that fought him, One amaterasu and he was down and out.