The question, then, is about when you have a party that wins second place in the popular vote but forms government, that's a problem. Yes, that can be a problem. Ideally, we wouldn't like that. It's rare, but it happens. But I can point to other problems in other systems. When you have a centrist party that gets to make a coalition or be in a minority position regardless of what happens to its vote share, that also would be a problem. That's why I put forward a metric of the responsiveness between shifts in power with respect to shifts in votes.
I'm a little uneasy talking about what the voters' will is. Remember that these results of wrong-winner governments come about mostly because of the accumulation of votes, not just within ridings, but mostly the aggregation across ridings, so it could be that one party won very big in some ridings and very small in others. These distortions can happen either at the electoral stage—where that's what happens in the first past the post—or they can happen at the parliamentary stage, when you have a proportional system that generates the need to form coalitions.
There is a recent paper by G. Bingham Powell, of the University of Rochester, that basically says the propensity for these sorts of—what shall we call them—distortions to emerge is about equal under the two systems, it's just that they occur in different places in the electoral process. In the proportional system, they're almost always going to have to occur in the parliamentary formation of coalition governments, where parties could conceivably lose votes, yet because their ideological location gives them a bargaining advantage, they get into cabinet. Would we call that a distortion?
That's why I'm saying I'm a little.... We're making choices in a less-than-perfect world, so there is no first best electoral system. This is akin to buying the used car that you can. No matter which electoral system you get, it's like a used car. It's going to have some dings in it, and you're going to discover some of those problems once you drive it for a little while.