The article is either mis-informed or (knowing McCullough) willfully bending the truth.

Suppose Justin Trudeau’s Liberals were to lose their parliamentary plurality in the next election and be replaced by a Conservative one. In that case, Trudeau could cite this expansive theory of incumbent prerogative to remain in power for months, rather than concede defeat and hand the reins to a Conservative administration. This would award him ample time to hammer out a legislative agreement with one of parliament’s third or fourth place parties, then convene a parliamentary sitting at the latest possible moment to ratify the arrangement and extend his stay in power even longer.

If a Liberal government can get confidence through agreements with minor parties, they are, by definition, the government. There is no need to concede just because you don't have the most seats.

For decades, the clear Canadian norm has been for the party with the most seats to install a prime minister — and promptly after an election.

This is what has normally happened, but is not a norm. Just look at BC in 2017 when the 2nd-largest party formed government with the support of a 3rd party.

Since Canada has three or four center-left parties but only one center-right one, it was perhaps inevitable that the former would eventually conclude that some manner of co-operation could permanently shut out the latter.

What does this even mean? We had more than one party on the right and they merged to improve their chances of winning.

The moment it becomes a settled progressive consensus that a Conservative minority government must never be permitted to assume power, the Tories’ only remaining strategy will be to win an uncontestable parliamentary landslide of the sort they presently seem nowhere close to achieving.

If the Conservatives can't get the confidence of the house, they are free to win more seats or appeal to other parties. Not a problem with the system.