Power is different than saber skills. Anakin, as of ROTS had the most power, just not the most mastery or experience. GL even said, "At the time of ROTS, Anakin is the most powerful Jedi, he just lacks the experience." Even in RODV it states, "Once the most powerful knight ever known to the Jedi Order, he is now a disciple of the darkside, a lord of the dreaded Sith, and the avenging right hand of the galaxy's ruthless new Emperor."
So anyway you cut it, Anakin is able (though not guaranteed) to beat anyone in saber combat, as of ROTS.
As far as sending OB1 to fight Anakin...there could be multiple reasons. OB1 couldn't beat Sidious, maybe Yoda was hoping that OB1's connection to Anakin would help (which it did in a way), or maybe he thought Anakin could beat him and figured that could be the end of the Jedi. There's alot of reasons. It doesn't negate the fact that Anakin could beat Yoda.