If everyone on Twitter, Facebook, and Youtube is talking about something, people will be talking about it on TikTok. If they aren't, that is noticeable and that too will be something people will talk about. That can actually lead to more attention on that platform due to the Streisand effect.
The primary concern would be if all the social networks censor the same thing, but that isn't a concern here due to the opposing political views unless your concern about censorship is just these platforms not allowing extreme violence, but that isn't what the article is discussing.
1) “Wtf, why’s your dog laying on a nail??” “It doesn’t hurt enough yet” 2) YouTube is paying people enough that they make a good living and questioning the policies means potentially risking their bills not getting paid.
Three of those platforms are American-controlled and one is Chinese-controlled. Even if all four have "effective censorship", it seems unlikely that American-controlled and Chinese-controlled platforms will block/manipulate in the same way and to the same end.
This is not a fixed set either – every few years, a new platform pops up. Tiktok is a relatively recent example, Instagram an earlier one.
If content restriction gets too heavy-handed, people will respond by moving to new platforms which are less restrictive – at least in free(-ish) countries. I personally think that inconsistent and overly heavy-handed moderation – punishing too many users by algorithm for innocent or trivial things, even while reports against other users doing seemingly much more serious things are dismissed – is one of the factors behind Facebook's recent slide in users.
Added to that, many people on the political right (30-40% of the population) view these platforms as politically biased against them, and are keen to find new places without that perceived bias. Attempts at establishing more conservative-friendly platforms generally come unstuck by being overrun by extremists (neo-Nazis, antisemites, etc) who push mainstream right-wing users away, and also through pure incompetence (both technical and business). But I think it is likely that sooner or later someone is going to come up with the right balance to succeed in that space.
The common idea is to assume that “the masses” move slowly, but the reality is that when properly motivated everyone wakes up early and changes technology in a matter of hours. Many of them bringing their followers with them with only the last of the followers being the ones moving slowly.
I understand your point, but I think the platform is relevant. There are four platforms that have a considerable number of users (TikTok, Youtube, Twitter, Facebook/Instagram), and they all have provenly effective censorship, especially optimized over the past couple of years. If it's one of those four, it does matter.
I would also claim that the platform is only irrelevant if removing that platform results in a negligible reduction in views. Removing TikTok removes 1/4 of the services, and probably the vast majority of younger eyes.