We can't "proportionally" represent a constituency which returns a single individual

So, if you want PR you have to either: Have two distinct classes of MP: Some were directly elected and represent an area, others are just to make the up proportions - but obviously these are just worse right? Second class MPs.

OR Abolish the constituencies entirely, now nobody represents your area and its particular concerns, or everybody does, which as we know amounts to the same thing because of how dilution works.

Unlike other electoral reforms a PR system has deeper implications far beyond the elections themselves. Historically the UK actually didn't have a single electoral system for every constituency, and that was fine†, indeed it works fine in the US today, the thing which needs to be coherent is what happens after the election and PR meddles with that.

† Well, not "fine", this is the era of the famous "Rotten Boroughs" but the fact that the system varies from one place to another wasn't key there.

It also means that people are voting for party lists, not individuals, and the lists are controlled by the parties. In a proper parliamentary system the parliamentarians directly represent their voters, and have a mandate from them. Parties do not have that, only MPs have that. By passing the mandate from the representative to the party, and the party having list control, that puts far too much power over parliamentarians in the hands of unelected party functionaries that draw up the lists and have no mandate themselves.