I don't think the centralization and security must be mutually exclusive. So long as the alternative is _also_ secure, it's a win-win. But that's the big problem.
Suppose Apple makes devices and has an app store, but you're not required to use their app store, and then if someone can coerce Apple to censor something, anyone can route around it by using one of the others who can't be coerced, e.g. because they operate in a different jurisdiction. That's not centralized; there is no single party who can serve as a chokepoint for the bad guys to set up their nefarious surveillance/censorship apparatus.
Now suppose that only one company has an app store for a given platform, or the alternatives only exist on paper because there are too many barriers for ordinary people to use something else and then the one store still has 99% market share, or they use their control over the device to exclude apps even if you use a different store. That's still centralized and that type of centralization has to be broken in order to solve the problem.
Suppose Apple makes devices and has an app store, but you're not required to use their app store, and then if someone can coerce Apple to censor something, anyone can route around it by using one of the others who can't be coerced, e.g. because they operate in a different jurisdiction. That's not centralized; there is no single party who can serve as a chokepoint for the bad guys to set up their nefarious surveillance/censorship apparatus.
Now suppose that only one company has an app store for a given platform, or the alternatives only exist on paper because there are too many barriers for ordinary people to use something else and then the one store still has 99% market share, or they use their control over the device to exclude apps even if you use a different store. That's still centralized and that type of centralization has to be broken in order to solve the problem.