I realize that Thai doesn't have 5th freedom rights, but if the plane is packed from ATH, it means that the market is in ATH, not GVA. On the flights to and from GVA you see how many people who travel too BKK and these numbers are not very impressive. The load figures to GVA might not justify the extension from ATH, but I suppose the yield might.
As I pointed out, I got the figures from a friend, but I'll see if he can supply us with further info
I suppose that you can find the configuration on Thai's website.