Theonik
Member
The main advantage of constituencies is it encourages local politics. Constituencies choose from a small set of candidates that are supposed to have some relevance with them and the local populace can interact and become familiar with them.Most election systems, including the Westminster one, are designed to fudge the result into making a parliamental majorities easier in the name of governability. The fact they are arbitrary and biased doesn't make your idea any better
Local MPs are meant to represent their voters and are accountable to them. Voters cannot be expected to recognise every MP running for every party but knowing local MPs is practical. This relationship is vital to ensure that every MP is directly elected by a constituency.
Mind other countries have proportional representation using multi-seat constituencies so it's not impossible. Greece works like this with 48 constituencies filling up 300 seats. (before a bonus 50 seats were awarded to the first party that was a newer reform which is quite controversial and is looking to be repealed only for parties to back down.)