First of all, if anyone bother to look at the report, it Assume US initiate 10% of trade tariff and THE WORLD, NOT JUST CHINA, retaliate.
In this case, then yes, US will lose, but in reality, it is very unlikely the world would be standing on Chinese side. In fact, most country in the world would not retaliate to US trade tariff or were actually exempted. So in the end, how much different that can made to damage US economy is very light.
Second of all. If US and China have a trade war, both side suffer, end of story.
There WILL not be a worldwide response with US trade war. It would be quite naïve to think otherwise.
And a US-China trade war is indeed beneficial to US economy, because in this case, the definition of Trade War stands, China have more trade surplus than US, and by that definition, it will benefit the US.
EU have already applies for many exemption, many of them have already granted, and many of them are being considered. On the other hand, would EU grant exemption to China under anti-dumping? That mean the reality is different than what you imagine...