I think Skyrim is in fact a perfect AID to getting people into Glorantha, rather than a barrier! If I have a new player, it's where I go to.
With new players/GMs, there's a really, really high chance they have played and enjoyed Skyrim. It's a great starting point if you're someone who prefers their Sartarites to be more Saxon or Celtic and your Lunars more Roman (as they have been through much of Glorantha's RPG history).
Both Skyrim and Glorantha (originally) pull from similar historical source material. Despite recent shifts, the Lunars always had a strong Roman element. Legions, Centurions, Vexillae - these words were not chosen accidentally. Likewise the use of Saxon and Celtic terms and concepts in the creation of Sartar. Same with Skyrim. These elements were used because the authors and their audiences (with the general cultural background of white western culture) by and large have a stronger familiarity with Rome and its imperial activities than many other ancient cultures.
From a marketing point of view (and this is an area I have considerable experience with), Chaosium would be much better served moving TOWARDS the 'Romans vs Vikings plus Dragons' space, not just based on Skyrim but in a general sense of attracting people from the main base of Western fantasy consumers - as these tropes are ones that people cleave to.
That's if just making money is the goal in the quickest and easiest fashion by relating to existing elements your potential clients are familiar with, however.
At this point I want to make it very clear there is nothing WRONG with doing that. There's no moral or intellectual superiority in treading a less mainstream path, despite what many people tell themselves. There's no innate cultural superiority between the Iliad and 'Married at First Sight', much as that might be a good thing. Selling Glorantha as 'Skyrim with SO MUCH MORE' is a great way to get people to give you their money, and in a business sense that's generally a good thing.
Now obviously more recent owners of the property and their artists have pulled it in a different direction, so using Skyrim as a touchstone is only more viable if you use older materials or if you're waving YGMV rather aggressively at new people.
But this does bring up the question of marketing Glorantha rather than playing it. And while related, these are not the same thing.
What you do with your game once you are playing it is generally a function of how a GM and their players interact. If all my players love Skyrim, I'm going to probably GM Glorantha in that direction, rather than 'force' them to see the world as I feel it should be seen, or as current source materials depict it. Other GMs may do that differently. That's about what your game table wants and will sustain. That's playing Glorantha.
Marketing Glorantha is getting people to play it. And that's where the conversation moves towards managing people's preconceptions and attachments. And this is about new players, not existing ones.
From a branding point of view, YGMV is not a good thing necessarily. Brand cohesiveness is very much a thing, and YGMV gives that a nasty kicking. It's the default expectation across almost all human cultures that I am aware of, because most people consume and engage with cultural items in a progressive fashion.
If you're selling Glorantha with YGMV up front, then you're selling it to a very small minority audience. You're basically saying 'Here's a new brand for you to interact with, it's got some solid cornerstones but you can stick whatever you like in between those'. Some people will like this concept but that is most certainly a minority. That's not necessarily a bad thing - while in general terms you may sell fewer units/encourage fewer new players than a more 'traditional' brand approach, if that market is over saturated (either in the true sense of a financial market or the marketplace of your players' minds) and you feel your product may not compete sufficiently, then aiming outside the box is a valid approach as long as you can break even or profit from that market share (either by selling books or getting people to enjoy playing with you). And more importantly, YOU (as either a GM or a person making money from selling books) have your own personal stake in things and you get to choose what level of risk/reward you want to satisfy your own desires.
If you're not upfronting YGMV but selling Glorantha in its current 'form', then that's something else. You're selling a unique setting with visual and cultural themes that diverge quite widely from the Western European norms that dominate fantasy tropes and again, that's selling to a minority audience. And again, not necessarily a bad thing in a saturated market.
That's why this is an interesting question every time it comes up, because from a marketing/branding point of view it's certainly not the 'traditional' path to success.
It's hard to measure the 'overall' success of this choice because that's something that takes a long time to observe and requires data that no one will have at this point in time, if ever.
I don't know the sales figures for Glorantha products in recent years but even if I did, I'd not use that as an accurate measure as there's no way to cleanly tell how many of those sales are growth (entirely new players and GMs) and how many are from existing Glorantha players, with a good few decades worth of exposure there. And in brand terms, it's very difficult to draw a line in the sand and delineate a product success path (which is sustainable longevity over a given period) for Glorantha, given the various and not inconsiderable shifts in system and visual styles, which are major defining elements of RPG products.
The success of marketing Glorantha to new players, and the role of YGMV in that, is something that will take years, or decades to examine and even then, you're highly unlikely to ever pull hard data. The closest you'd come is when you feel the majority of the 'old school' players have shuffled off (mortal coil or otherwise and don't worry, I'm included in this grouping!) and you examine whether the game is selling and playing sustainably to a 'new' generation. And since it's a continuum, that's basically just an exercise in arbitrarily kicking some numbers in relation to the relative financial framework of whoever owns the property at a given point in time, which may be of intense interest to them but isn't necessarily connected to an 'overall' examination of the 'success' or 'longevity' of a property.