> Forgive me but this employee/labour analogy seems to be talking a bit past my concerns.

I'm not sure which analogy you refer to. They are literally employees in every sense of the word. There is no analogy – that is straight up what it is.

> then multiple additional MPs are elected to make the overall composition of the house proportional to the votes cast.

You improve the proportion of labour union representation, perhaps, which we have already talked about, but why are we selecting employees based on their labour union membership in the first place? If you hire people at your private sector job, do you elect them based on their labour union affiliation? Or do you elect based on your understanding of how they will represent your organization, selecting the worker who you feel will do the best job?