Australia certainly deserves what it gets (my home country) given its attitude towards debt and housing, but I think the contagion is real.
A China 'slowdown' will probably not hurt the US, in fact, it may give the US leverage.
A China 'crash' will surely have emotional contagion among investors, which of course matters, because if they pull the plug on activities it'll translate into real world effects ...
But the 'material' contagion of a Chinese crash ... it's harder to predict.
I suggest that the issue is far more likely to be damaging as a 'trigger' to a bubble burst or something else, rather than materially damaging in and of itself.
Again, it could burst some kind of bubble and start a recession, but a China slowdown itself is not enough.
If the problem was with chinese real-estate, yes, the risk for contagion was minimal.
The only way that the economy "grows" indefinitely is if it regularly dips, and that is exactly how it has been working since WWII, with dips/recessions at 1975, 1982, 1991 and 2009.
It's surreal watching our major parties both trying to claim credit for the global economic climate.
It will badly hurt the largest economies in the world, which all depend on trade. If we're lucky it won't lead to global war.