I'll admit, my knee-jerk reaction to hearing this statement (especially from a media critic YouTuber...like, what's the point of your job, then) was a resounding 'FALSE' and I stand by that even now.
HOWEVER...I think it's possible to make a legitimate case for it. ^^ I'd like to see if anyone here who does think it's 'True' can come up with something better than the vague 'as long as it feels good to you' reasoning that they offered. So let's take a vote:
So I do think it's False, but with an asterisk: I think the statement itself is basically a strawman, in context.
'Bad' is such a vague quality (if you take it in a literal sense); it can mean any negative thing that you want it to, especially when applied to art. So in this case, I believe the speaker decided 'bad writing' meant 'writing that doesn't suit everyone's tastes'...which is all writing, and if all writing is bad then none of it is. Leading to the conclusion in the title.
The dissonance comes from the fact that they've spent their literal entire career using 'bad writing' to mean 'unskilled writing that many readers will find confusing, disappointing, or unpleasant due to its blatant disregard for convention'...which is what people usually mean when they say 'bad writing', and is a thing that definitely exists. :T
I assume they suddenly decided to go with the weird definition because a fan was asking how to avoid bad writing, and they wanted to say something that sounded nice and encouraging. But idk; maybe it's just me, but I don't think cute platitudes are as encouraging as an honest answer. Like, they're asking you to use your skills as a critic to help them form writing strategies; there's nothing mean about doing the thing they probably subscribed to you for. Of all the times to suddenly become lenient and ambiguous, the moment a novice writer asks you point-blank what NOT to do is the worst possible time. It really felt like they were just blatantly lying.
If I were to try to answer the question, I think first I would point out how vague it is (there's a billion ways in which writing can be bad, and a billion ways in which those things can be avoided or reworked into good things) and then, I'd tell them to feed their inner critic. To consume lots of criticism, positive and negative, especially about the media they like, and once they feel ready, to start forming their own. If you get yourself to a point where you can give an articulate answer when asked why you think a piece of writing is good or bad, you'll be able to do it for your own writing. You may even be able to do it while you write, weighing your decisions as you introduce them, and predicting how they might affect the rest of the story.
IMO, bad writing tends to be isolated writing. Like, you can hear/read it and immediately clock that the author had no idea how it would sound to anyone living outside of their head. Or outside of their circle of friends, as the case may be...keep yourself open to new perspectives on a regular basis, learn to interrogate writing instead of taking it at face value (again, even when you like it) and I think you'll naturally improve.