The parent comment said, "The system that puts legislators into place is a local majority vote, which is just as flawed as a national majority vote. It leads to a 2-party system which concentrates power and typically results in corruption." Reduced to a pair of logical statements:

  Local majority vote --> Two-party system
  National majority vote --> Two-party system

The parent poster did not make a statement of either of these forms:

  National majority vote <--> Two-party system
  Two-party system --> National majority vote

Thus, the previous poster is not arguing that only a national majority vote leads to a two-party system. In other words, a national majority vote is a sufficient but not necessary condition to have a two-party system. At best, we can infer that the parent poster intends to say that a majority vote on any scale leads to a two-party system, whether local, electoral college, or national, but even that was not explicitly stated.

I understand the logic of my parent's statement. To rephrase my question: We have a two-party system, and we do not have a national majority vote. Therefore, in absence of other evidence, I must assume there is a low upper bound to the importance of a majority vote on our two-party system.