I believe his point is that until Wikipedia proved it could work, allowing everybody to edit was seen as impossible, as way too risky to work.
I know you don't like to hear it, but to me, as somebody who started pushing wikis before Wikipedia existed, your arguments against the possibility of broadening adminship sound regrettably like the arguments I used to get (and, amazingly, still get) about how open-to-anybody editing is impossible.
I understand what you're saying, but I think I've found the flaw in your argument. You are saying that Wikipedia has proven all the people that said a wiki could never work wrong - I'm not sure that's the case.
Wikipedia has shown that a pure wiki doesn't work (beyond a certain size). We've had to introduce blocks and protection, both of which go against the idea of a wiki. We've compromised, and as such have managed to make a viable website.
Wikipedia is not a pure wiki, it's the closest we've managed to stay to a wiki without causing problems that are beyond our ability to manage. We've managed to stay very close, but we have had to step away in order to solve a few problems. Adminship is the main way we've done that.
The proposal for opening up adminship is basically a proposal to move back to a pure wiki. Wikipedia started off as a pure wiki, and it worked ok at first, but as it grew it get unmanageable and required the creation of admins.
There have been multiple requests for evidence that opening up adminship won't work - pre-admin Wikipedia is that evidence. It didn't work, and that's why admins were created in the first place.