You're forgetting that GF focuses a lot on their home market (Japan), so if they were willing to give the Japanese fans only three days to pick a starter based on their middle evolutions, I can easily see them willing to do so to the worldwide fans. Besides, I'm sure that they've caught on to the fact that Corocoro leaks days early by now, so we'll actually have 8-5 days. The same goes for a video reveal...some of them have been leaked a day or two earlier.
You do have a point, but I still see it as too short of a timeframe to make a final decision on a starter.