The other flaw is the assumption that a third party that got 10% of the votes would then get 10% of the Senate and House seats. The reality is that they would get 0% of the Senate seats, but would have an outside chance to get a handful of seats in the House. The development of an alternative party that has a chance of electing a president would be a long, long uphill climb, and I believe would make things much worse before they ever had a chance to get better.