I agree with you in general, although in the Westminster model, you usually have two parties that swap power and a distant third that on very rare occasions can play a kingmaker role. At the end of the day, it's all the same. Conservatives and liberals, however they are constituted (and sometimes the liberals may cross the line into some degree of socialism, aka Britain in the post-war period up until New Labour's victory in 1997) simply swap places.
What has exacerbated the situation in the United States is the way in which the two major political parties have so thoroughly taken over the voting system itself. I think back to the 2000 election where you had a Republican in Florida (Katherine Harris) actually responsible for certifying election results. When you have a close race like in 2000, whether she's the finest most upstanding person or not, it calls into question the validity of the whole process. While other countries usually have a central non-partisan election authority that manages elections and certifies results, in the US, the constitutional division of powers between states and the federal government basically allow the very voting system itself to be undermined, if in appearance alone, by partisan concerns.
Then there is gerrymandering, which happens in a number of countries besides the United States, which can heavily distort elections. In some ways the US is a century or more behind other industrialized democracies, although a certain amount of gerrymandering does go on elsewhere.
This has been the chief argument for the party list proportional representation system, in that it largely removes the temptation to gerrymander. Parties have to campaign to get representatives elected, and it becomes much more difficult to rig the voting system so that certain districts are created that will tend towards one party or another.
FPTP is just a bloody awful system. It tends to disenfranchise an enormous number of voters, and it basically allows major political parties to game the system to their benefit.