I do agree with you that MapleEngineer is being silly. You can’t just dismiss Canadian Dimension because it’s “on the left”. Frankly, the best Canadian journalism is on the left, including The Tyee, The Narwhal, Canadaland, Literary Review of Canada, etc.
That said, I think these labels can be useful. I doubt you would object so strongly if someone pointed out that Rebel News is far right. If I didn’t know what Rebel News was, I would consider that useful information. I would sooner say that reality has a left leaning bias than deny that a news source is left leaning.