> Votes are cast because it's assumed Americans wouldn't support a party that simply nominated a candidate via authoritarianism or autocracy
No, the modern candidate selection process in each of the major parties isn't an abstract response to theoretical concerns about what Americans would respond to, but a concrete response to real issues identified through previous nomination processes.
> If anything, "wisdom of the mob" voting is more reflective of the Republican party's process
No, it's not; the Republican Party process is designed to artificially create an insurmountable perception of momentum for the early leader because of experience about how early lead usually favors the institutional candidate, and the set of early primaries and caucuses favor, more than the country generally, the establishment faction of the party, so that this provides both the right candidate and a short competitive part of the primary with an early shift to general election campaigning. The Democratic system through 2016 (changes are planned for 2020 in response to 2016) in general design (pushing committed superdelegate counts into horserace delegate coverage hasn't historically been the norm) favors a longer competitive period and broader geographic competition but provides a safeguard against a hung convention. Each of these has failure modes—if superdelegates commit early and the media included them in horserace coverage, the Democratic system gets the same kind of artificial inevitability as the Republican system. If a celebrity candidate sucks up early attention with a large but weak field where establishment support is divided, the Republican method work against the establishment and lock in the same kind of advantage for the celebrity it is designed to for an establishment candidate. And if a well-funded establishment decides to take that fight down to the wire with whoever it has standing after the early winnowing, it can drag out into a long primary fight if the type the system is designed to avoid.