Get rid of FPTP and the Electoral College that enables a two-party stranglehold. If a vote for a third party wasn't a wasted vote, we could see nuanced parties and politicians emerge that don't have to tow a party line.
FPTP is what makes Reform so dangerous though. They have a real chance of having a lot of power. In a proportional representation system where parties have to share power in coalitions these extreme parties actually have to be involved in government, at which point they’re exposed as completely incompetent. See the Netherlands right now for example. I would rather have these extreme positions represented, because they will be represented poorly. It takes wind out of the populist sails, where they can no longer simply promise everything until they’re in power and completely destroy the country.
I think FPTP ends up working out a lot different in the parliamentary context. The US only has 2 parties in Congress, despite FPTP.
In terms of strength of 3rd parties, I'd say they are generally quite weak in the US system, somewhat stronger in a proportional representation parliamentary system, and potentially overpowered in a FPTP parliament like in the UK.
Historically I believe the 2-party system in the US was pretty good at tamping down on extremism, but recently the 2 major parties have acquired too many extremists.
Does it? Could you explain which mechanism you suggest using? Because the main results from social choice theory about ranked choice voting that come to mind seem to be all about impossibility of fair elections (eg Arrow) or even paradoxical situations such as cyclic preferences (eg Condorcet).