Despite your claims to the contrary, the truth is that we don't know whether the experiment will continue to work or not. But so far it is working, and every month that passes by where it continues to work increases the chances for continued success. There are risks: the dwindling numbers of full-nodes, mining centralization, core development centralization, etc.; however, there's also a growing community of talented people passionately working to address these risks. If it does work--if Bitcoin remains decentralized and continues to grow--then not only will it represent a great advancement for economic freedom, but it will also put that trillion-dollar pie in the sky within arm's reach.
The size of the user base and the price are not important for the experiment. But the distribution of mining power is.
Only if
1. The mining power is abused. That hasn't happened yet in any significant way, so Peter R's argument applies equally. Every month that passes without abuse increases the chances for continued success, albeit slightly.
2. The distribution of mining power is stable. The real world evidence suggests the contrary. Yet you ignore it.
those 4 companies (which may actually be only 3, or 1, or may become 1 next year)
Or may become 10. Funny how you didn't include that possibility in your rhetoric. I wonder why.