> Why is there any notion of acceptability for a company’s rulings on how their copyrights should be protected?
From a legal perspective, there's not, companies can attack copyright infringement even if they don't do it in a moral or acceptable way.
However, from a legal perspective, emulators don't violate copyright and neither do videos teaching people how to use them. So if we want to talk about the acceptability of Nintendo claiming copyright on emulator videos, and if we want talk about the morality of emulating systems that are current-gen, and if we want to talk about the "typical use case" of emulation, then we're not really talking about laws anymore. In the context of those questions, it is valid to talk about whether or not a company's motivations are "acceptable", because we're not talking about legality.
The law is already settled on this point, building and distributing emulators is legal activity, even for current-generation systems. Social convention/responsibility are the only things people can debate about emulators. And legally speaking, at least a portion of these videos are probably fine (of course, Nintendo is unlikely to be called out on this because nobody wants to get sued even wrongfully over a Youtube video). We can debate whether or not they're responsible to make and post online, and we can debate whether or not they contribute to piracy, but legally they're probably not copyright infringement.
Nintendo is under no legal obligation to wield its copyright acceptably or responsibly, but also people who build emulators are under no legal obligation to make sure that no one pirates Nintendo games. I don't like how these conversations often get framed in a way where Nintendo is judged only on its legal obligations, but people who build and talk about emulators are judged on subjective social responsibilities that have nothing to do with the law.