Well I hope you understand that when I say that I am skeptical the list is complete and ask for your source so I can look at their methodology, just saying "my source is a redditor" without even their username or a link to where they said it isn't going to make me less skeptical.
Also I have found at least one mass shooting he missed thanks to a podcast I happened to be listening to
https://canadiantruecrime.ca/episodes/2018/3/12/21-ernest-desroches So no, his list of per 91 mass shootings was not complete.
As for media coverage, you seem to have missed my point. It's not just that there is more coverage of mass shootings today, and yes violent crime does get much more coverage today, but that the coverage is much easier to find. Finding every incident where more then one person was shot requires a massive amount of work reading through old newspapers and missing stuff is very easy. I've seen other people claim to have exhaustive lists of all Canadian mass murders only to find they missed some, including very big ones.
Also your redditor seems to have a very broad definition of what a mass shooting is. Normally by Mass Shooting someone means a pseudocommando rampage, where a single angry individual goes on a shooting spree in a public setting as an act of revenge on society or terrorism. However your redditor instead seems to define mass shooting as any incident where at least two people were shot, and as a result includes a number of incidents that don't resemble what is normally thought of as a mass shooting such as violence in families, bar fights, gang warfare, armed robberies that went wrong etc
For example redditor includes the sheddon massacre. This was a coup d'etat in the Bandidos motorcycle gang where members where lured to a meeting in the countryside then disarmed and killed one by one, not what is usually meant by "mass shooting".
I have a hard time believing that before 1991 Canada had zero examples of incidents like the Duke of York Tavern shooting, where a guy got into a bar fight, left and got a gun from his friend and returned to shoot the people he had been fighting with wounding bystanders in the process before 91, especially since the homicide rate back then was twice what it is today.
Most of these incidents are over far to quickly for law enforcement to intervene so I doubt that greater experience could be the reason for lots of of small shootings appear on your list in recent years but not in earlier ones. The study you linked to before on the other hand gives a much narrower definition of mass shooting, closer to what is normally meant by the term, but the averages can be thrown off by one or two very large mass shootings like the Oslo massacre.
With such a broad definition of mass shooting we would probably get a better picture by dropping lists of incidents and focusing on gun violence or homicide rates in general, which in Canada have been falling steadily since the 1970s.