Its in the title...
I don't get how its some surprise that it is obito, just because he fought with the fourth doesn't mean he is on the fourths level or anything. he took a giant rasengan to the back and got stabbed opposed to doing any damage to minato himself. he clearly had guidance under madara which is how he learned how to cast a genjutsu on the nine tails and made him a stronger ninja not some loser like he was.
point is: i just don't think tobi is strong he has a space time jutsu thats it...nothing massive like the MS abilities madara itachi or sasuke have, he doesn't have sage mode(jir, kabuto, orochimaru) or a killing move like (i.e. Rasengan, chidori) madara makes him look like complete shit. the only thing he has in my opinion is NOW the rinnegan which he only has used the outer path to control the tailed beasts he failed to use the preta path when naruto rasenganed his dome.
the only thing that makes him "strong" is that he can slip through people and make it nearly impossible to hit him and he can suck someone up and put them in a dimension. to me that isn't strength thats just an over powered defense...he resorted to using izanagi on konan.
if he was fighting someone one on one without slipping through his opponent neji could beat him high difficulty, again just cause he fought minato doesn't mean he is on his level so don't pull that card saying "obito was a weakling he could not have fought the fourth" ...all he did was slip through him...didnt do any damage to him at all.
bring on the flame.
EDIT: Okay neji was just an example i just threw his name in there cause he's probably the strongest of the K11, but my argument is not that he is strong w kamui and weak without it, i am trying to say that he hasn't displayed any abilities that make him on level with someone of naruto, sasuke, minato, nagato, etc which is what everyone tries to make him cut out to be. slipping through objects is just a defense he doesn't have any offensive power. hence why i said minato beat his ass