Certainly bitcoin is immune (mostly) to central bank manipulation for better or for worse - I think that’s a given. But any currency can enter deflationary regimes, as witnessed by central bankers’ desire to intervene during recessions. It’s not clear that the properties of bitcoin make it any more or less vulnerable to this.
As an aside I’d say the factual evidence of the efficacy of central banking is controversial; many would put as much blame for historic and recent recessions on central banks as would credit them for the recovery. Certainly bitcoin by its philosophy and design is pretty skeptical about central bankers and their motivations.