Gadol, you’re mixing up the Rambam with the sefer yereim. The latter holds that a man is allowed to physically discipline his wife. Other rishonim hold that way too, but the Rambam makes no mention of it, and neither does shulchan aruch. Like all methods of mussar, they are subject to the ultimate question of if it will work – in today’s age, and really for the past 200 years, the answer to that is a resounding “no.” It does not work. It’s not wrong in principle, because there were rishonim who mention it, and if it works to ensure that the wife adheres to halacha, why is it any different than beis din beating people to comply with halacha?