While the post-mortem [1] is lacking (mostly in terms of follow-up), my read was that the network was simply overloaded to the point where validators were crashing, not that some critical centralized component went down. I'd imagine there's similar DoS attacks one could execute against the older chains (but probably much harder to find given their maturity).

I suppose if you wanted to make an argument against decentralization on Solana it would be that it seems low-probability near-term that there would ever be an alternative validator implementation due to the complexity of Solana and VC-funded nature of the main one (it could always be forked though, I suppose).

[1] https://solana.com/news/9-14-network-outage-initial-overview