Perhaps the Golden Age had to deal with the fact that the Jedi had not seen the Sith in so long, that they had become convinced that they didn't even exist.
I apologize, but I must insist that this line of thought has no factual basis to it. Why, exactly, would not facing a Sith Lord be relevant to a 'Golden Age' for the Jedi? Especially when -- according to Labyrinth of Evil -- the dark side of the Force had been increasing dramatically in strength two hundred years prior to Revenge of the Sith to pave the way for Darth Sidious's reign. Once again, all evidence concludes that 'Golden Age' refers to the Jedi's combat ability.
And a good explanation for the way the Jedi fought in the OT movies has a lot to deal with the age and experience of the characters. Obi-Wan had been extensively training in the Force, not lightsaber skill and physical training. Luke had no formal lightsaber training, save his deflection practices with a Remote. A comparison can be made, because the OT "Jedi" were of a broken order with no combat practice in decades and only constant meditation.
A comparison cannot be made because George Lucas has said that there are no real Jedi in the OT. In order to make a comparison, there must be two like terms. In this case, there would have to be two sets of 'real Jedi' -- if it were referring to choreography. That Lucas cites that there are 'no real Jedi' in the OT by virtue of lightsaber combat would debunk the theory of a comparison.
I don't have skills in seeing the future, yet I know that enemy infantry must come into a walled-off battlefield through the entrance.
This is irrelevant. That the audience is aware of something that the characters are not -- even if it is something obvious -- has no bearing that, for virtue of the plot, that the characters themselves should know it. I can't see into the future, either, and yet I know that it's pretty stupid to offer one's self as bait after giving my enemy the location of my semi-operational battlestation, which I'm currently on. Yet Emperor Palpatine did it. Is he suddenly retarded or sub-par? No. He made a mistake, a foolish, blatant mistake but it happens. Jedi are no different.
Yes, they lacked the proper Jedi foresight they should of had, but it doesn't take a genius to have basic battle instincts. If you have a battalion of soldiers wielding melee weapons and have limited range, move them into tighter formations, especially if they have an ability to halt ranged attacks from the enemy.
We see such stupid mistakes in science fiction movies and horror flicks all the time. How the villain monologues and reveals to the hero his diabolical scheme; how the war-hardened soldier always makes that one fatal peek around the corner; how the hero is subjected to a ridiculously overzealous death trap because the villain is arrogant. It's merely plot induced stupidity excused by the fact that characters (heroes, villains, and even Jedi) make mistakes -- even if they are painfully obvious.
Yet Obi-Wan, while off-balance as you can see, managed to do a backflip over Greivous and slice off two of his hands in under a minute. And Obi-Wan also used one of the most basic Force maneuvers, Force Push, to completely incapacitate him and disable his ability to fight with a lightsaber.
As Darth Hord has already instructed, Obi-Wan was selected by Mace Windu to battle General Grievous because he was the best-equipped to do so. Soresu is basic, simple -- it's defensive. Yet Obi-Wan mastered it to the highest level. What supreme battle tactics could Grievous use against him? Just the typical "smash, break, destroy" to break his defenses. That is why Obi-Wan outmatched Grievous in dueling ability. His form is specifically designed to deal with such examples of unrefined feats of strength.
As for the Force push, it was already made clear that Grievous was simply too clever and too cunning to be in a situation where a Force push could be used, in most cases.
You've provided adequate arguments for Sidious, beside the quote of George Lucas, so I won't even attempt to argue against it. However, note that most of Sidious' God-like powers were utilized during the DE period, not the Prequel. During the Prequel Era, Sidious was merely a Sith Lord using influence to cloud the Jedi's foresight and judgement and to manipulate the courts and Anakin. He didn't summon these black holes and storms that his clone managed to, and that was WAY after the Prequel Era.
You're confusing the issue again. You're confusing feats with power. You're right, Darth Sidious's PT Force attacks do not compare with his reborn persona; but that was never the issue. It was Sidious's effect on the Force -- the thing that required the Chosen One to remove him from existence. He was never "just a Sith Lord" because no Sith Lord ever had the same effect on the Force that he did. Ever. Not Exar Kun. Not Darth Revan. Not Marka Ragnos.
Let me know how RE: Extinction is. And I'm not a skilled debater in comparison to you, Janus, Advent (granted she throws insults and accusations much too easily, and a few others here.
Extinction was great. Albert Wesker makes an appearance. And, yes, you're a talented debater. You just have to understand that quotes -- even if they're blanket quotes -- still apply when directed by a high enough source.