You haven't actually pointed out lots of scenes where Palpatine "acted stupidly." You've simply declared that he was handed victory through no action of his own but the whims of a contrived script. But with all due respect to your personal tastes, the bottom line is that Vader isn't a comparable manipulator and strategist to the man who manipulated a galaxy simply because Vader altered terms of an agreement with Lando Calrissian. I suggest we go with the reason actually ascribed: namely that Luke had the potential to surpass Vader as a Force user and Palpatine is constantly seeking the shiniest tool. Surely you're not suggesting that superior Force power is determined by... fashion? You're moving the goalpost: Force mastery isn't determined by what one happens to be wearing and while I absolutely agree that Jedi and Sith Masters should be decked out in full armor at all times, your argument is wafer-thin. And this, too, is indicative of inferior Force power? Generally, a "quote war" challenging Palpatine is a doomed enterprise for reasons you've already acknowledged. But that's the point, isn't it? Palpatine has the better feats and the better quotes. I would recommend interpreting the scene as it has been interpreted by canon authorities: that Vader exploited a momentary position of weakness in Sidious, who was distracted and unsuspecting, and managed to slay him... while dying in the process. Pointing out that Vader was missing a hand and had a gimp leg in an attempt to exaggerate the extent of his victory somewhat undermined by the fact that he's a 7' cyborg with superhuman strength. I could just as easily say it's embarrassing that he died at all wrestling a 5'9" octogenarian. In other words, put Sidious and Vader in a boxing ring and Sidious comes out winning every time. He's simply more powerful and that has been demonstrated again and again and again. More accurately, you seem to prefer him when he is depicted in a single scene in one of the five films in which we see him. In Revenge of the Sith, Palpatine shows greater power and skill than film!Vader ever did.