Ballot access makes 3rd parties more difficult than does a winner take all system.
The 2 parties in power must submit zero for their candidates to appear on a ballot.
A 3rd party must submit, in a national campaign, a total of something like 1.3 million signatures, depending on the states and their terribly non-uniform requirements. This is not counting the legal hurdles that must be overcome just to qualify to submit the petitions. Then there are requirements about signatures, collectors, forms, etc.
IF 3rd parties were so innocuous, there would be no good reason to have these legal hurdles in place preventing others from joining the game.
More fair, probably, is for all slots on the ballot to be write-in slots. Period. That leaves it entirely up to the voter whom to vote for. Those who run solid campaigns will be known, and those who don’t won’t.
A serious 3rd party should have no trouble with ballot access. The Libertarians often don't even get .5% of the vote, yet I believe they are on the ballot in all 50 states most cycles. There are too many fringe nutters and vanity candidates to loosen ballot access too much.
The Tea Party, for example, has millions of supporters and could easily have become a real political party. It isn't because the vast majority of people realize it would be a dumb thing to do as it would simple split the right of center vote. Actually, that is an example of just how easy it is to get on the ballot. Many fake Tea Party's sprung up (funded by the left) designed specifically to split their opposition.
Geeze, American's Elect doesn't even know what they stand for other than "moderation" and don't have any candidates lined up at all, yet they are already on the ballot in like half the states and working to be on the ballot in all 50. Ross Perot's party even hung around for awhile.
3rd party's just don't work in our winner take all system that doesn't allow for coalition building.