This doesn't disagree with what I said. What I meant is that the Venn diagram of "Short chapters" would fit almost entirely inside "Web comic", which is a problem because we want to avoid adding tags that basically by default come with another tag. That's just poor design.
I don't see anything wrong with a reasonable degree of tag overlap if it helps users get more relevant search results. If anything, having one tag cover such a wide variety of content is the bigger problem, as otherwise "Web Comic" as a tag loses most of its relevancy in facilitating a search. There's a significant enough style/format difference between the majority of web comics and these 1-2 page twitter chapters to warrant the distinction. Especially with this volume of content, as it's not like this is asking for a niche tag that only covers a couple dozen chapters.
If we're worried about tag overlap, how about Isekai and Fantasy? Not all Fantasy is Isekai, but the overwhelming majority of Isekai is Fantasy, almost to the point that it makes Isekai pointless as a genre. Unless you're trying to exclude it to search for non-Isekai Fantasy, which is basically what a "Short" or similar tag would allow us to exclude from Web Comic.
There's tons of other examples of tags with just as much, if not more, overlap than Web Comic and Twitter. Villainess and Reincarnation, Romance and Drama, Wuxia and Martial Arts, Monsters and Zombies, etc.
Edit: Though I suppose there are also policy/standards controls that could address some of these concerns, like defining "Web Comic" as excluding "Long Strip" Manwha/Manhua-style series, or specifying that the more specific "Zombie" tag precludes use of the broader "Monster" tag, but that's also not a perfect solution.