LOL.
That's Moebian-Hyperborean cartoon art from the era when it was cool. Nothing historical at all in it, but lots of pop/pulp culture and French Bandes dessinées.
And this is what I find so cool in Glorantha: it's totally intertextual, deeply layered, extremely personal. You cannot just read certain Gloranthan opera as The One True Glorantha, because they too are interpretations, choices, and lots and lots and lots and lots of retconning the present IP-holders' attitudes and opinions back into certain older publications, and not retconning it back to others.
I think the crux of this is in the Gloranthan names, which are a total hodgepodge of English, Bible names, funny fantasy names, and totally uncool fantasy names which are cool because they start to sound real after repeating them a lot. For example, Sartar has Jonstown. 'Jon' is a Biblical name Ioannes (that I think is it's Greek form. The Hebrew would be still different), and Jon/John was a gaming friend of Greg. 'Town' is English, although phonetically really close to the German Zaun (fence, both relying back to 'boundary', ie. land defined to belong to someone/some group). And now I hear someone say Alda-Chur means 'Far Place'. No, I bet it comes either from Old English 'Old Church', or was invented as a cool sounding fantasy name and nothing more. Someone want to translate 'Jonstown' into Sartarite and retcon its etymology???
But it's OK, because Glorantha is a creation of its time, and American at that, and even if Tolkien had invented real languages and real names in his world, most 70's and 80's fantasy didn't. So read it as a product of its time.
And in general, we don't play in fantasy settings because we want to follow rules. We play because we want to create our own. And the tradition and livelihood of Glorantha has always been YGMV, or rather YGWV. And I've learned so much from people whose interpretations differ from mine.
For example, my Glorantha is forever coloured by Purcell's front art on Apple Lane. The cousin of Donald Duck in 15/16th century body armour and carrying a same era crossbow? Totally incorrect, I hear you say. Yet conveying a lot of meaning: Glorantha has these Duck people, and they can be really badass!
Canon is a veil. The compromise. The net of Arachne Solara. A drastic resolution full of holes and just barely binding enough of the world together to keep it from destroying itself. And thus canon is super important, although not something that people actually see and worship.
Sorry for the rant. This is totally opinioned.