1. These problems caused actual confusion for real developers doing ordinary web development work. One of the linked questions has hundreds of thousands of views.
2. You suggest I'm being a pedantic dick to people who are "helping others", but W3Schools doesn't help anyone - at least compared to the counterfactual of them not existing. It would hypothetically be right to say "okay, they have errors, but they're better than nothing" if the realistic alternative was "nothing". But the realistic alternative is that MDN would rise to the top of search results. The complaints about W3Schools' accuracy come in the context of them having skillfully SEOed their content above basically everything else, including huge amounts of not-for-profit content that is vastly superior to theirs. That does cause their very existence to do damage to the world, and make them worthy targets of criticism.
3. Remedying the point about the behaviour of colspan in real browsers being misdocumented doesn't require W3Schools to "write a novel" about anything. It just requires to them to remove content they've included which is false.