How many times has capitalism become dictatorships or fascists?
A handful of times. Most capitalist nations are not authoritarian. Purely by the numbers, it has a much better track record. Of course, “it’s not real capitalism/communism” always derails this discussion.
I think you outline why communism inevitably fails. Marx advocated for violent revolution to overthrow the “bourgeois” democracy. The moment democracy is gone, the strong take and retain power. This is why, no matter the system, democracy must be the bottom line. It ensures that power is distributed. It’s not perfect, but it’s much better than the alternatives.