The hardcore driving game players are posting their disappointments and frustrations, I agree. But just as many of them are seemingly fine with the delay. Take a look around the forums; there's a lot of noise from both sides.
Honestly, I wouldn't have a percentage. That's impossible to know. It's why I made sure to lead off with "I think". Even our entire registered member list is about 1/20 of the GT6 sales numbers.
Those are all good questions: I don't have answers, and neither do you. I can tell you that IGN reels in multiple times our monthly number of viewers, and that's not counting how many people would hear their news on Youtube. They cast a very, very wide net, and word travels fast.
Too true with that last sentence, though. It seems every game comes pre-loaded with Brands, Silverstone, and the 'Ring now. Lovely circuits and all, but it means there's so much overlap these days.
I think the Course Creator had the potential to be a game-changer, but it didn't pan out (the 21-month wait did it no favours). I think a merging of manufacturer's more in-depth configurators and a game like Forza or GT would be fantastic: I'm told TDU2 did something like that, but with more realism it'd add even more to the immersion factor.
I also believe VR will have a huge affect on the genre, possibly more than anything that's come before. The major drawbacks are that it's pricey, and not everybody can use it without getting sick. But after trying it, I'm convinced.
A yearly release schedule isn't the answer, I'd agree. That's probably why we don't see it in the genre outside of F1 and NASCAR: Forza does it in name only, as the Horizon and Motorsport series are quite different. I could certainly make the argument for T10 extending things to a three-year interval for each franchise, but the current two is hardly bad: the differences between FM5 and FM6 are massive. I just went back to FM5 earlier this week to grab some achievements, and it feels like a different game to FM6; easily more so than the gap between GT5 and GT6, for instance.