It would have been better for both Yoda and Obi-Wan to face off with Sidious together. Sidious obviously had a powerful advantage in his fight against Yoda because he was wielding the dark side. So it's not like the Jedi would be dishonorable to even the playing field with two-again-one (happened in The Phantom Menace when Qui-Gon and Obi-Wan faced off with Maul).

At least that way Sidious wouldn't be so inclined to mess around like an idiot during the duel (which in ROTS, he did, and it made it harder to take the consequences of the duel seriously). Lol.