Not only that, in France for example the liter of Diesel fuel was always 10 to 15 euro cents cheaper at the petrol station due to how regular gasoline and diesel fuel was taxed.

That's why before EVs started to show up on the market en masse if you walked into a dealership they would always recommend that you pick the diesel engine if you wanted to save money of fuel costs.

That was actually the reason why the Yellow vest protests started in 2018 when the French government announced that the taxation gap between diesel and regular gasoline was going to disappear gradually.

Small edit to add to the context:

By that point, when the protests started in 2018, the governments(right and left) of France and the many French automakers had been pushing diesel engines as THE solution to alleviate rising fuel costs and so justifiably, the protesters thought that someone had just pulled the rug from underneath them.

Also this measure was in direct contradiction to Macron's campaign promise which was that he was going to reduce the tax burden or at least not increase it on the middle class, especially the rural middle-class that basically cannot get a job without having a car as public transport is almost non-existent in rural France.

That and many other things which I won't get into since it is not relevant for this discussion really riled people up.

In Canada, diesel fuel is priced around mid-grade gasoline (89). So it's slightly more expensive than regular, but slightly cheaper than premium (91/93).

Based on this, I've always thought of diesel as "more expensive", like you better get 15% more power/miles out of it if it's going to cost more! However, I suspect that most people purchasing diesel vehicles have as their other choice a car that would slurp premium, so for those buyers perhaps diesel is still a discount, even in Canada.