Making these distinctions is often quite difficult, because particular behaviours by voters or by politicians frequently embody both elements. Other than in grand coalition situation, any government that is formed is going to be a partial selection from the entirety of the House. You want to ask yourself how representative the governments in question are of the totality of the House; or if not of the totality of the House, do they at least, as the saying goes, cover the median member of the House in terms of, say, a left/right or other distribution?
One of the peculiarities of Canada is that for much of its history, it's the only single-member district system in which much of the time the government has covered the median. The standard form of government under first past the post is a party that is off centre, which doesn't cover the centre, and is able to govern nonetheless. The critical check is that it is vulnerable to defeat. One hopes that down the road there will be a sufficient alternation to keeps the system on course. That's one thing.
The particular worry that is often expressed in relation to PR systems is that they often empower small minorities to be the pivot for coalition formation. That's terrific if there is a party that is itself of the centre, and in effect can be the pivot for government, helping perhaps along in alternation. That was the story in Germany, for example, until the nineties basically. The Free Democratic Party in particular, was in every German government. It typically had two of the most important ministries, foreign affairs and economics. Whether it was a Social Democratic or Christian Democratic chancellor, the FDP in some sense kept the ship of the German state, so to speak, on a kind of course. That's not true now. In fact, two of the last three elections have forced a grand coalition in Germany. That does make for a kind of consensus politics, but it produces a really unsatisfactory electoral situation when you have the debate between the chancellor and chancellor candidate of the other party and their cabinet colleagues.