Dooku shot lighting at Yoda and he had no trouble deflecting it. As far as offensive attacks, with the exception of Palpatine, I thought Yoda should have been able to overpower most opponents with either force pushing them hard enough like he did against the red guards in ROTS, or with some kind of "light side" energy projection to incapacitate, not kill. Maybe go full Profesor X and do a mental attack, which is less violent.
When I saw the OT, I never saw Yoda as a fighter. First of all, he was a puppet, and he could barely walk because of his old age. He was like the Dalai Lama or Gandhi. A reclusive, wise figure that guided people if they could find him. He was all about knowledge and wisdom, not combat. Not once did I see him (I could be wrong) teaching Luke how to be more proficient with a lightsaber. His training was more introspective and mental. Maybe that's why Luke lost his hand.
Then again, when I first saw the OT, I had no knowledge of the Jedi Order or what role they played in the galaxy, because all the Jedi were dead, with the exception of Obi Wan, who had a lightsaber, had fought in the Clone Wars, and his description of what a Jedi Knight was seemed different in my mind than what it was shown in the PT. Seeing Yoda as a council leader in those large temples with all that access to technology and presumably financial wealth was strange for me. All of a sudden, the Jedi looked more like the Catholic Church , and the Jedi Knights were Priests or Monk like figures. Still, as weird as it all was, I still didn't see Yoda as a fighter. He was in a room making decisions or "meditating"...probably sleeping.
Maybe in the EU Yoda was shown as a fighter before the PT came out, but I didn't read those books or comics, so perhaps it's my own fault, due to my own lack of understanding or ignorance on the subject. That's the problem when the mythology is a mystery, and you let the audience create their own ideas about that fictional world, that by the time the filmmakers finally explore that mythology like they did in the PT, it just doesn't match the fan expectations.