To what extent does your analysis rest on the assertion that bitcoin can
... arbitrarily be changed by some guy on a random whim when he wakes up in the morning...
Because that is really not a fair summary of the situation. Which I am sure you know without me telling you. But I wonder whether your analysis is fully settled (in your own mind) ...
Even if you don't assume it centralizes through economy of scale, or that mining cartels or other special interest groups take over, another event occurred just recently that many people did not pick up on with legislation in Japan (that will obviously happen everywhere else too). Govt is a monopoly on force, and cryptocurrency does not supercede political interests or the only consensus system in the real world (force). Whoever controls the courts controls what bitcoin turns into. Here is the Japanese legislation:
"Only approved virtual currencies by the authority are considered legitimate and can be traded, sold or promoted to public"
This means govt is the legal arbitrator of forks. The US, UK, and EU will hold a meeting and all collude saying only the fork with chain anchor or worse is the real bitcoin! Since they can easily control the exchanges and mining pools, people will be forced to use that fork or have their coins become worthless. The only reason bitcoin isn't illegal is because they know how easy it is to co-opt and morph it into their cashless society control grid.