Lucas literally stated point blank that Yoda never fights anybody and that he wouldn't be any good if he did.
There are deleted scenes from ESB where Luke is swinging his lightsaber while Yoda is on his back because that was all Yoda was ever supposed to do with regard to combat: instruct. Not demonstrate. Not fight.
I agree with what your saying but i think thats cause they couldnt film the puppet with the saber and so he just was making up rationale for it. Otherwise he never would have yoda swinging one in the pt as soon as the technology became available. PM yoda still a puppet no saber atoc cgi saber i dont think its a coincidence