I'm not sure this argument really holds. In the United States, third parties can have a significant influence on elections by siphoning off votes (see, Nader or maybe Perot), but they tend to have much more muted effects on policy. I would argue that Andrew Yang did more for the cause of the UBI as a loser in a widely-watched Democratic presidential primary than he would have been able to as a third-party candidate struggling to qualify for the ballot in most states. If his new goal is to focus on ranked-choice voting, I struggle to understand why the calculus would be any different.

I agree with you in wishing we had more than two parties to choose from; for one, studies have shown that negative partisanship is much lower in democracies with more than two major parties.