FPTP has a well documented effect of producing a 2 party system (along with numerous other issues): https://en.wikipedia.org/wiki/First-past-the-post_voting#Two...
RCV works and is simple to understand.
It's so obviously superior that it's facing substantial rejection: https://responsivegov.org/statement-voters-reject-ranked-cho...
I don't see how either of these assertions follow.
The size of the mandate is important, and the connection between a 2 party "system" and FPTP is something that you'd need to elaborate upon, because there is nothing about the ballot as such stipulating the number of parties. I. Fact, other parties are frequently on the ballot, so the dominance of 2 parties is not obviously connected to FPTP as such.