Lung cancer has not changed overall numbers all that much from 1990. https://seer.cancer.gov/statfacts/html/lungb.html So, no it's not responsible for the massive drop in cancer deaths by age group.
I included HPV and Stomach cancer in a PS specifically because they are minor changes to overall numbers. Sunscreen also impacts the rates people get cancer, but it's a very minor effect.
And lung cancer is not the only cancer caused by smoking.
In any case, cancer death rates and changes in risk factors do not speak directly to the claim about treatment effectiveness. If you are diagnosed with cancer, you are basically every bit as f'ed today as you were 50 years ago, except in the special case that your cancer happens to be one of those that never would have been noticed back then.
Notice that Male at the bottom of the cart women are only down 17%. That makes the impact on overall numbers significantly lower. It's also a chart of deaths, what you want to support the idea that treatment is useless is a chart of new cases.
Also, see that huge drop in Prostate and Colorectum cancer. Yea, that has nothing to do with smoking it's almost completely related to better treatment making a huge difference.
And again, we are not looking at equivalent populations. The older the US population the worse cancer numbers look in absolute terms.
So, even the chart you are using to support your argument actually supports mine.
PS: To account for a 25% drop in cancer deaths lung cancers could have hit zero in that cart and it would still not be enough.
I included HPV and Stomach cancer in a PS specifically because they are minor changes to overall numbers. Sunscreen also impacts the rates people get cancer, but it's a very minor effect.