I agree that Yoda and Palpatine seemed pretty evenly matched in the movie. Yoda just gave up because he lost his midichlorian cloak.
That or he just got too demoralized, because I honestly don't see how falling down or losing his lightsaber temporarily, or the impending arrival of a squad of Stormtroopers would really have mattered too much to Yoda. I mean it's YODA!
Anyway, as far as taking the novels over the movies, that's fine, but that's not the canon policy of LucasFilm or of Lucas himself. The movies ARE Star Wars. Everything else is subserviant to that. Even the novelisation of ROTS is based on the story by George Lucas and the screenplay, but written by somebody else. Approved by Lucas of course, but not the movie, and thus not his "definitive vision" of it. Personal taste aside of course.
IIRC, according to Lucas, in the ROTS audio commentary and perhaps elsewhere in quotations, he says that Palpatine did NOT throw the fight. His plan was to kill Windu like the other Jedi, but Windu was more than a match for him. Read the novel, he was having trouble fighting him, and we can see that Windu was getting the upper hand on him. What was the "deception" was his acting old and feeble in front of Anakin to gain sympathy (please don't let him kill me, I can't hold on any longer... I'm too weak, oh I'm weak, etc). That was playacting. Clearly his lightning wasn't doing any good against Windu since it was all getting blasted back in his face.
According to Lucas the powers Palpy was using wore him down and the stress on his body is what resulted in his "change." It's not that lightning hitting you automatically makes you look old, because it never did that to Yoda or Anakin or Windu. His teeth turn rotten and his fingernails turn long and dirty. Clearly its a change on his whole body, not just his face. He's able bodied, but we know that old people can be able bodied thanks to the force in the prequels. Basically there's a few theories rattling around... that Palpatine was actually much older than he looked and was using the Force to keep his body looking "younger" than normal, and he had to give up this extra power while he was fighting Windu AND blocking his own lightning (or he'd have been hurting himself more than he was with his own bolts and stopped sooner). Another theory is that he kept calling on more and more power and that was what "aged him" rapidly. So even though he's only a 63 year old man, he looks like he's over a hundred thanks to the strain (and I suppose again absorbing his own energy too).
You'd think he could just re-adjust his aim and hit Windu instead of stupidly hitting himself over and over, but perhaps Windu was using the force to channel all the lightning into the energy blade, just as Yoda may have done so into that glowing thing in his hand(s).
So what would have happened if Anakin hadn't shown up? I think he would have been forced to keep fighting and Windu may have killed him after all (since he decided that Palpy was too dangerous to be left alive after all, though his original intention was to simply take him into custody). Did Palpatine, sensing Anakin showing up, decide he'd play weak to gain sympathy? Surely. If Anakin hadn't shown up I think he'd have tried to keep fighting or roll away, perhaps getting klilled int he process. But that's different than saying that he dilberately "threw the fight" and that he'd have killed Windu easily. Lucas didn't intend for us to think that.