Both Shiraishi and Atobe have everything they need to beat Gin consistently. The main reason is what Tristan outlined in the France D2 match. If you're up against a player who specializes in power, but whose other stats don't measure up, just hit away from them and they won't be able to wind up. This doesn't guarantee that Gin will never hit a Hadokyuu, but it won't be often.
On the points that Gin does manage to hit a Hadokyuu, there's no reason to actually return the shot. Shiraishi/Atobe can just let go of the racket. We don't see this utilized very often because power players are usually matched up against each other, where they actually have to face the opponent's power more or less head-on, but Higa D2 provides an example.
Beyond that though, all the top players have additional tools that would tilt matches with Gin in their favor. We know that there's a way to neutralize Hadokyuu completely. Shiraishi is probably either aware of it from practicing with Gin or would be able to figure it out reasonably quickly, and Atobe should be able to find the same method with Insight.
That being said, the HS power players tend to be more dangerous, even among their peers, because their stats besides power aren't bad at all. It's still possible to use the same tactics against the likes of Duke, Albert and Randy, but there's a much higher skill requirement to do it consistently.
