Interesting. I'm at 228 races, 7 wins, 18 poles, 8 fastest laps. I was stuck at 3 wins for a while, but my SR dropped back to C after some tough races, and I got 4 more wins coming back up, mostly at SR-B. One thing I did notice...I can't say for sure that it's real, is that it seems that if you're within about 3% of the top ten in your region, you'll get fast guys in your race and get gridded mid pack. A little slower and you end up being "best of the rest" and don't get those really fast guys. Unfortunately, it's impossible to tell where the line may be.
What it really comes down to is luck of the draw, and driving talent. My first few races were humbling. Last time I played G&T was with GT 4. There was no GT online, and I was always among the fastest of my friends that played. Big fish in a small pond. Well, the pond is now an ocean, and I'm not the fastest guy. Give me a track I've got a handle on, and some laps, and I can do well. I hope to crack the top 100 in my region, and maybe make page 1 on the worlds. I've accepted that I'm no alien, and I'm old, so I'm not as fast as I once was. On that point, I think the biggest difference is that, though I can put in a fast lap, it's harder to hold it together for a whole race.
Not everyone is fast enough to win. Even a new DR-E with lots of talent can come in and beat a guy with 1000 races under their belt.
Edit: my best advice is make sure you recognize and take advantage of the oppertunities that come up. If you grid top 5, and the people behind are slower than you by .5 seconds or more, you have a chance to get away with the front group. Be patient, let tires warm and drivers settle on lap 1, but take advantage if someone goes wide. Be consistant and don't follow too close. Many times, if you get away with the leaders and laptimes are similar, it's the guy that makes it to the end without doing something stupid that wins.