Bitcoin is meaningfully decentralized because miners alone do not decide the fate of Bitcoin - there are also users, businesses, and developers as major actros. The 51%++ actor cannot kill Bitcoin, only cause inconvenience. The worst that could happen is a successful DoS that would force a hard fork to another PoW algorithm.

PS1 The full nodes are actually very well decentralized.

PS2 The physical hash power is skewed towards China, which is not ideal, but it tends to decentralize to US, Canada and to lesser extent other countries. It is improving.