Most of that is just wrong.
The CDC has famously been forbidden from funding studies into firearm deaths for decades. This has not, of course, affected any other country in the world, and outside of the US there are innumerable analyses demonstrating how effective gun control can be.
With regards to the Lancet paper…none of what you’ve presented actually argues against any of these policies. At best, you could argue that the impact won’t be 90% — which is honestly a fair position to take. 90% is the highest estimate. My guess would be much less than that. But even a 10% reduction would cause a vast decline in the number of gun deaths in the US.
It’s a long road, but you first have to take a single step.
P.S. if you actually take the time to read the WaPost article you’ve linked to, Hemenway doesn’t call the research “crap” he merely points out that this is a very high estimate and that he’s skeptical that the benefit would be 90% from just those 3 laws.