Decentralization doesn't really help, it only creates more bubbles.
Reddit is extremely centralized, and you can find hundreds of subreddits that do cover Israel's ethnic cleansing. However, most popular subreddits are heavily censored, while the smaller communities become an echo chamber, and often get radicalized.
Decentralized bubbles are still bubbles—even worse, since the barrier to entry is higher.
Giving users control over the bubble, rather than one company, is the important part.
Is it? How does it help with radicalization? If anything it makes it worse, since people on the extreme political spectrum will always try harder than the regulars, while companies care only about that sweet, sweet money that comes from being bland and attracting the masses.
Don't get me wrong, I care deeply about privacy and want a decentralized works, but it comes with its own cans of worms.
The goal for distributed moderation is not to prevent radicalization, but to prevent one rich man from controlling the content people see. As a user, I can opt into whether I want to see terfs or developers or movie spoilers online or not. I think it's important for users to have more tools and agency over their online experiences.
There are other factors in play though that I think help create less polarising and radical social networks - ability to create custom homepage feeds gives to more variety and less control by the platform maker to sway audiences. Non-commercial networks (which doesn't count Bluesky) have less incentives to juice engagement. More distributed networks have levers audiences can pull if the main developers steer the network in the wrong direction.
> since people on the extreme political spectrum will always try harder than the regulars
Imagine if anyone could create an alternate feed algorithm that penalises these try-hards which people could subscribe to and use instead of the default.
It's a good and necessary thing to become "radicalized" in order to prevent genocide and break out from the pacifying programming of the state. the state puts pressure on centralized social media companies to enact clever methods of censorship to pacify the masses for them. such companies might even just willingly self-censor in anticipation out of obedience or just plain uncritical acceptance of state department propaganda.
So the state and the ruling class produced a radicalization of the masses themselves where the status quo is to pretend that genocide is normal - a "zone of interest" type of effect is supposed to be part of what's "normal". While I agree with you that decentralization is not a silver bullet, because it can create pockets of echo chambers, it's still a good tool for communities to be independent from certain influences like from the state or corporate culture.
I'm not singling out this kind of radicalization, but any kind, including alt-right, qanon, etc.
I'd say that inaccessible bubbles become echo chambers of people screaming into the void. The point is the be visible and heard, and federation does the opposite.
LinkedIn's approach has been to segregate pro-Palestinian content to a bubble where it's not shown to people outside it. Now, that is believed to be because they are deliberately trying to limit pro-Palestinian liberation content due to the extremely pro-apartheid and pro-occupation beliefs of their CPO Tomer Cohen, but it's none the less pretty effective.