Sometimes, unfair political systems are salvific
We complain, rightly, about gerrymandering that means Dems get more votes in US House elections but far fewer seats. Maybe we might empathize, while of course never sympathizing, with xenophobic loons UKIP who got 13% of the UK vote and <0.2% of the voice in its parliament. We could even congratulate the SNP, who managed the reverse feat in getting <5% of the vote and about 9% of the seats (although still zero power to affect governance just like UKIP)
Now this is not a fable on US 3rd parties. Our system is different for a start and all UK non-RW parties added together would still have lost handily, so vote splitting seems moot, but it does tell us that even far more popular parties than any US based potential 3rd is likely to achieve for decades, even in an arguably fairer system, face great challenges in becoming relevant. UKIP's growth in vote share was triple the SNP's, and far more than triple anybody else's. They are now the 3rd vote getter and nipping at the heels of being half the size of Labour by vote count. But they don't have the broad strength needed to gain seats. 13% of every constituency (not the reality, but an illustration) still means no seats, whereas Labour getting only a bit over twice the votes gets 230 times the MPs because they have many areas where the majorities and pluralities are safely Labour.
So let's be careful about wishing for different systems. Would anybody want Nigel Farage to have 13% of the say in Britain's legislation (in a PR system, he would have been a hero not a loser)?