Nvidia's primary customers are those who won't switch no matter what which makes up a vast majority of the market. There are TONS of users out there who won't consider AMD no matter what. AMD is just dead to them.
I don't doubt if 10 months from now, even if FreeSync is EXACTLY the same as Gsync, the general consensus around the average consumer is that Gsync is better. AMD doesn't push their products as well as Nvidia and that's a fact that we can all attest to quite easily.
This is true, we can agree on this point.
I used to see too many gamers with money order systems with Titan SLI when there's the 780Ti (1080p monitors in their builds!).. because "It's more expensive, it must be better!"..
Even when I advised them they could save a lot of $ by going with R290X (in Australia, the price delta is ridiculous), but they say either "I only want NV, cos they are the best" or "AMD is a cheap brand, I don't want that in my rig".
Strangely enough of late I didn't hear many "AMD drivers sucks" comments. A few years back that was the most common response.
Saying that, at some points AMD GPUs did held a good chunk of the market, even ~50% IIRC with the 5800 series. So definitely there's a lot of folks out there who are willing to switch if NV doesn't perform. G-Sync premium tax would be a major factor for these switchers.