Bluesky is at least semi-decentralized
No it isn't, this is marketing and until the developers actually put their money where their mouth is and provide the genuine capacity for decentralization (not just along some narrow technical definition but actually decentralized in practice) this is pure marketing hype that you absolutely shouldn't trust until you are given indisputable proof and then you should still be skeptical because they can always pull the rug out from under you.
Bluesky is open source yes, but what they are talking about is the CLIENT side of Bluesky, the actual system is dependent upon proprietary code that is most definitely not open source.