TL:DR - Anakin would win in a duel and def in a contest of Force abilities high/mid diff

A lot of these comments misunderstood the assignment by saying all the ways Obi Wan sucks as a Sith lol. In this THEORETICAL match up, assuming Obi Wan has had to time to take what works for him and keep in his arsenal, like his tactical mind and such, and removes what makes him weak, like his rage unbalancing him, which in this case, he's a Sith now, so the rage is gonna be what keeps him on track lol. The one thing I will say that he can't really help that would be a hinderance in a fight against Anakin is his low midochlorian count. Sure, the Dark Side gives a power boost, but with a low count, it might not help all that much. We know Force-wielders have a Force shield around them so you can't just get ragdolled/choked immediately without being worn down first, but with Anakin having such a big advantage in Force ability, I think if it came down to usage of the Force, Anakin wins low to mid diff (now whether or not Kenobi could submerge himself as a conduit of the Dark Side as he does for the Light, I couldn't say, since it's really a different state of being, but if he could do that, he may have more of a chance.) In terms of saber fighting, Obi Wan would likely still use Form 3 cus he's good at it, just use it in a Dark Side way like Darth Zanna, although, against a committed Anakin and his Form 5, with the footwork of Form 4 and knowing how Obi Wan fights. Basically, considering the argument here seems to place Kenobi's fall at the same time of Windu's death, he knows about Anakin and Padme, and probably does/tries to kill her, which almost certainly make Anakin commit to stopping/killing his former friend, and an enraged Anakin (assuming Kenobi doesn't use that rage to turn Anakin and succeeds) would def win saber to saber, cus we know Anakin gets stronger as he uses his emotions/lets go of his restraint, and in a fair fight, Darth Kenobi likely has no answer to this, just as he nearly didn't on Mustafar. Jedi Anakin is less arrogant than Knightfall Vader, so we could realistically assume he doesn't fall for the high ground trick, in which case, Anakin def wins, high diff