What great coup has Chuck made? He thinks he’s got a tape with Jimmy confessing to a felony. But Jimmy already has an out, he can torpedo whole tape by claiming that he was making up a confession to try to get his brother to snap out of his latest insanity. It’s certainly plausible - Chuck says so on the recording. Jimmy has evidence that he isn’t out to screw his brother, if he wanted to take advantage of Chuck he could have just had Chuck committed like the doctor wanted but didn’t. Sure he gets Jimmy to say on the tape that it’s for real, but it’s not like he’s actually under oath. Meanwhile, Howard has to be worried about Chuck’s stability after the quit, and probably has been grilling Ernesto about what’s going on. Howard doesn’t have Chuck or Kim’s insight into Jimmy, so probably thinks that doctoring documents is way beyond what Jimmy would do, especially since he knows Jimmy could have had Chuck committed twice if he really wanted to destroy Chuck.
So you’ve got a guy who dresses like a baked potato and rants about electric sensitivity while making paranoid claims about his brother trying to argue that his brother is dishonest enough to forge documents to undermine him but honest enough not to lie about forging documents. Meanwhile his brother will argue that he just said stuff to make foil man feel better, and that if he wanted to screw Chuck over he could have just had him committed. I think Chuck trying to out-Jimmy Jimmy is going to backfire horribly.
Also, my opinion of Chuck dropped a lot with the reveal about their mother’s death and his outright lie about her dying words. His code of honor just conveniently vanished when it might cost him superiority points against Jimmy.