It wouldn't be the same pricing advantage at all. It would be so much cheaper that, actually, a lot more people would buy at $300 than $500, to the point where the total profit is higher. These are people who ordinarily wouldn't buy an off-contract phone at $500 but would at $300. You (both) seem to assume that markets are a zero sum game, i.e. that there is a fixed number of customers and you're simply stealing customers from other companies if you price lower than they do. But that isn't true; when you price lower than your competitor, you're not just taking their customers, you're also attracting people who have never been customers of either company before, because, previously, prices were too high for them to buy at all.
In fact, there actually is a fixed number of customers: the population of the country/region that you're selling into, and those customers are choosing to buy from you or your competitors based on your price. It isn't just a case of "Person A either wants a phone or doesn't; if they do then they will pick between all companies in the industry; if they don't want a phone then they won't look at the price at all". It's a case of "Person A either wants a phone at a particular price or they don't; if they do then they will buy at that price; if they don't then they will not buy at that price". The demand curve describes the number of people Q willing to pay a price P for the product. When you price at a certain level, you're just picking a point on the demand curve to sell into: if you price at P you will attract Q customers. The company decides roughly how many customers Q it wants, and then prices at P to sell that many units. Google decides how many phones it wants to sell, and then sets a price that will achieve this sales target. Indeed, I would expect Google of all companies to want to sell as many phones as possible, to as many different people as possible, even if it ate into their margins.
And don't think I'm just talking about the ever shrinking number of people who don't currently have a smartphone or off-contract phone either. Phones are, to some extent, a consumable: people won't just replace them when they are broken, but will replace them when they fancy a new phone and are convinced that the difference in quality is worth the price of the phone. The cheaper the phone, the more frequently people will replace their phone. If even top end phones cost no more than $100, then people would replace them every year or even more than that. Pricing at a lower price, therefore, increases the number of people who would be willing to upgrade immediately, rather than waiting a bit for a better differential in quality (or until their phone is rendered unusable in some way). It increases the size of the market without actually introducing new people into the market at all. So, yah, I simply don't accept that the relative price has any meaningful relationship to the price at which an individual company maximises their profits.
Finally, I know you're not talking about the rest of the industry, but the fact is that there are other players in the industry, and they all individually insist on pricing higher in the EU than the US. Again, I haven't heard any plausible reason for any of this.