A lot of liberal strategizing is based on the correct assumption that liberals won't hold their politicians accountable in meaningful ways as long as there is always a Greater Evil™ to worry about. If there were no Republican Party, the Dems would have to create one.
RCV would definitely be an improvement, and it would make third parties viable for Congress over time.
Systems like Proportional Representation would also help make third parities viable, but not something we could do with the way we elect Representatives under the constitution.
And, while I think RCV can do a lot of good in enabling third parties, I’m pretty dubious it can be used effectively for the Presidency, given the EC and the way elections are run entirely separately in each state.
So I think RCV could allow a different party to eventually break into the race, but I think with the EC, we’ll always have this state by state first past 270 system lurking under the hood