This 'not that sort of player' stuff crops up every time someone gets their leg broken and it's such an empty phrase. Martin Taylor. Ryan Shawcross. Neil Taylor. Always the same guff afterwards. "He's a good lad and he's absolutely gutted. There was no intention to seriously hurt anyone. He's not that sort of player."
Now I can see why people want to use the term to defend Son, because his foul was obviously not as forceful as a lot of those other incidents, and by current laws should probably have been a yellow card. But ultimately unless we are to believe there are psychopathic footballers who go around deliberately trying to break people's limbs, then it's completely meaningless. 'That sort of player' simply doesn't exist. Pleading that the severe consequences of these fouls weren't intentional is so obvious that it shouldn't need stating, and doesn't detract from the fact that they were reckless and, to varying degrees, endangered another player's safety.
Ultimately I think the best way to handle it is with harsher punishments for deliberate kicks or trips (and maybe even flagrant shirt pulls) with no intention of getting the ball. I can remember Xhaka getting sent off for something like that a couple of years ago, and I don't think there's anything wrong with it personally. I've already mentioned Guendouzi on Zaha, and there was one on Salah recently from I think Choudhury. And Son obviously. Just make things like that a red card in the laws.