I don't know how you got from my comment to China. I speculated that ranked choice might have more of an impact on which candidates are selected in primary elections. If you think voting for who will be the party's candidate is undemocratic then we're already there, that's already how it works, and I don't see anything in my comment that would lead to a single-party system like China. Maybe you could elaborate on why you think ranked choice in primary elections would take us to a single party system.

What I don't understand is why you think 3rd parties should rapidly gain power if they only have support from a fraction of the population. Why should their power be disproportionately larger than the # of people supporting them? I don't think it's very democratic to have a candidate with only 25% of the vote win the election.