The short answer is that, in practice, a huge proportion of Matrix activity is centralized, and they control it.
I thought that fell under the umbrella of common knowledge, so far as Matrix goes. If you've got data indicating otherwise, I'd find that interesting to see. I'm actually finding hard stats very difficult to locate (the few I can find seem incomplete, but corroborate this very strongly, for what they're worth), but again, I thought this was basically assumed to be true by Matrix users. I mean, if you search "matrix protocol" or "matrix chat" or "element chat" and follow the Happy Path of clicks to try it out, you'll have a Matrix.org account. The way you veer off that path? You have to know the address of another Matrix server. You won't be presented with other options, just the ability to type in the address of a different server. That this would result in Matrix.org having the lion's share of users seems a predictable outcome.
the “unblocking” requests to abuse@matrix.org are to remove the servers with spambot accounts from the blocklists we publish as matrix.org; nothing to do with centralisation.
As for the latter, that's immaterial—the more important it is to get server-to-server federation un-blocked with matrix.org, the more that can be taken as a sign of centralization. Moreover, if a large percentage of servers follow the Matrix.org blocklist, that's precisely the kind of centralized control the original poster was asking about.
(mind, none of this is intended as judgement, just clarifying why matrix.org would have substantial de facto "control" of the ecosystem & network, to use the original poster's word)
This was my point. We never blocked server-to-server federation with matrix.org. We published a blocklist of the abusive servers, and blocked them from the rooms which we manage on the server. There was never any centralised control applied, and there is no mechanism to do so (unless room/server admins opt in to using the blocklists we publish, but they are very welcome to use their own).