Loads of people said that about Twitter in 2006 when it was a "knock off." It's been proven wrong again and again. And Musk is the kind of guy who can create significantly large network effects and economies of scale.
Twitter has never been a knockoff experience, it was as different from the social media that succeeded before it as TikTok is from YouTube.
Meanwhile any number of near-exact replicas of it exist with a different flavor: freer speech, paid service, decentralized, specifically for particular political affiliations to name a few. None of them have made a dent.
But that just proves my point: they didn't make a dent because none of them had the network effects and economies of scale that a proposed alternative created by Musk would have.
Facebook (the thing I think people will agree destroyed MySpace) was not started by someone fed up with MySpace saying “I’m going to make the same thing, but I’ll moderate it differently!” It was started before MySpace had reached peak popularity, by an entrepreneur with a totally different product vision and way of looking at the world. Elon’s hypothetical Twitter-clone would probably be more like Gab, Parler or the Trump thing: Twitter, but with less moderation and some sort of weird gimmick, like “starting midnight Tuesday, I’m giving a free Model 3 to the first 1000 people who sign up!” or “I’m hosting a quarter of the load on servers on StarLink satellites!”
Twitter won’t be destroyed by someone making a slightly different Twitter clone, it’ll be destroyed by something that re-imagines entirely in a way that also supplants it, and it’ll probably come from someone we don’t know yet.
There is definitely a network effect around scale and populations of users.
Gettr seems to be making positive inroads on the conservative/libertarian population, particularly those for whom twitter is not an option due to previous banning/shadow-banning, and de-boosting.
As I expect there to be consolidation between truth social, gettr, parler, and others, think this will only get stronger.
Part of this is also that younger populations are preferring tiktok to Twitter imo.
(By “nobody” I mean both nearly 0% of users and only people who will not be missed on Twitter)