That's true of our two party Coke vs. Pepsi duopoly. Three parties is politically unstable but if we had four parties each with about 25% market share we could both vote more precisely and win more often. From left to right the parties would be socialist/communist party, Democrat government hireling party, Republican country club/business party, and the conservative party. Possibly by guaranteeing some seats in the state legislatures for the top four vote getting parties we could incubate a four party system.
Problem there is the socialist/commies will comfortably pair up with the Dems every time, so one way or the other that side will always be in.
Repub. country club and Conservative parties would fight like cats and neither would ever win.
There will never be that diversity in our system because, whether intentional or not, it is designed for 2 party's. That is the reason there has essentially ALWAYS been just 2 party's from the founding on. If one party becomes so rotten or useless it implodes, the new party that replaces it simply becomes the 2nd leg of a two party system.
The problem is there is no possibility of coalition building. So long as governing coalitions can not be built, people wisely realize that voting for 3rd party's simply dilutes the relative strength of their block of common interests. In essence, what this means is that more often than not Americans are voting AGAINST another party and are simply pooling their ideological strength to prevent something worse from taking power. It is extremely rare, especially at the national level, that the majority of Americans actually have someone they are really excited about voting FOR.