First Past The Post - Is it fit for purpose?

Many critics believe that First Past the Post or FPTP is a biased system, whereby the 'winner takes it all'. They believe that more proportional systems such as Additional Member System or Single Transferable Vote are more democratic.

In all honesty, FPTP is a majoritarian system where the party with the most votes/seats wins, and in 2011 when an alternative electoral system was suggested in a referendum, 68% of the turnout voted against it. There are positives about FPTP such as it keeps radical third parties out of power and it is easier for the electorate to understand (those who are allowed to vote at general elections).

Despite FPTP claiming to reflect the views of the majority, in 2010 we saw a huge failure with that claim as a coalition government was formed, which no one voted for. Also in question relating to the system is the definition of a majority? In the 2011 referendum, the turnout was 42.2% of the electorate. That is less than half of the electorate, deciding the electoral system under which the entirety of the UK must be governed... Is this fair?

I believe when there was acute political apathy, a two-party system and a smaller population, FPTP prospered in the UK. However, since the creation and popularity surge of third parties, the rise in population and rebirth of political interests, alternative systems such as AMS and STV have been particularly appealing. However, until turnouts of the electorate represent the majority of the UK, how can we know if FPTP is fit for purpose?