I think it depends on your goal. These videos are aimed at making you sound more like how most native speakers would typically speak. If your goal is to be able to connect with native speakers then I think you should take their advice, with a grain of salt (when you're ready for it of course, everyone moves at their own pace). Because the fact is that if you don't speak like a local/native, what ultimately comes across is that you don't speak the language well/you're not one of them. The more foreign-like and unusual you speak in regards to the local norms, the harder it is for them to connect with you, whether you or them, like it or not, whereas if you did speak more "typical speech", they would then automatically talk to you like you're just another local person. The more you speak like them, the more they'll treat you like one of their own and the further you are away from that, the less. Just the way it is.

(Also keep in mind every region has their own norms)

I would say don't stress about it too much. Listen/watch whatever like you usually do and certain words will naturally pop out to you. Look up the ones that you're curious about. Make sure learning vocabulary never feels gruesome and like a chore. Stay curious.

I think your point is fair when you say how natural something is is subjective when it comes to differing cultures of English speaking regions, but I think my point still stands when confined within one. But also to be fair to the people correcting these entries, if the person who wrote it hasn't made clear to which standard/regional dialect they wish their English to be corrected to (not putting the blame on them, just stating a fact), what you're talking about is inevitably the end result. At the end of the day, there is incompetency in both native speakers and non natives. Which would you rather rely on for the last word, an incompetent native or a non native claiming to be more fluent than they actually are? A phd educated native speaker or a C2 level foreigner? If someone is a non native claiming to be more fluent than they actually are and a native points it out, who would you rely on as a learner who doesn't know any better?There are spectrums for both parties.

I'll give it to you. If the learner's only goal is to merely pass an arbitrary exam, which usually only cares about absolute perfect grammar and not actually how well they can actually use the language, then sure go for the proper English that probably a non native could probably explain better, but if their goal is to actually communicate with natives in a genuine way...

Your question is way too general. It heavily depends on the field and it also heavily depends on what kind of a student you are and your own individual goals.

There are other reasons as to why people might not want to be corrected. A big one has to do with confidence. It's a well known fact that many people lack confidence when speaking a new language that they're just learning. Constantly pointing out their mistakes will only make them feel even less confident in speaking.