https://en.wikipedia.org/wiki/Porter_Airlines
In particular, airline monopoly control over allocation of terminal resources at an airport is not a useful prerequisite to generalize from. https://en.wikipedia.org/wiki/Porter_Airlines
In particular, airline monopoly control over allocation of terminal resources at an airport is not a useful prerequisite to generalize from.I did a quick skim of that wiki article (skimmed a couple sections, ctrl+f'd for "regulat" and "monopoly"), but couldn't find anything about a unique regulatory regime. There has been regulatory issues with the Toronto Island Airport (where porter wants to extend the runway to allow jets to land, but no one* else wants this), but I don't see where they required a unique regulatory regime?
JetBlue started in the late 90s, and according to the wiki [0], "was awarded 75 takeoff/landing slots".
Sunwing Airlines [1] started about 15 years ago, with departures from Toronto Pearson. They targeted the southern vacation niche. I don't know the details of the traffic capacity at Pearson, but they didn't get their landing slots by buying some other airline.
I'm not disagreeing with your comment about the limitations of dividing up a limited resource - many airports in North America are at capacity, and there's no room there for new competition to start up. But you followed it up with an absolute "You literally can't start an airline from scratch", which I took issue with because there are several examples that disprove it.