I think you're splitting hairs. Clearly "environment" in this context isn't the existence of Earth as a planet but life on Earth, the current ecology, and our place within it. That cares very much about how much total carbon output there is, regardless of what we perceive as fair. And again, as I mentioned, China's total energy use is likely artificially inflated than it might otherwise be because the world's manufacturing capacity is centered there - a fairer comparison would likely take carbon emissions used in exports and attribute that back to the home country that is importing the product. I suspect in that context USA & Europe will look remarkably worse per capita.
It may matter on academic considerations, people can discuss it, but it doesn't matter on global regulation layer whereby fairness is determined via collective consensus and for forseeable future, per capita is what everyone can live with. Your last point is signficiant because the rhetoric of total emissions isn't going to fly especially if the numbers make west look worse. In context of OPs post, trying to unilaterally frame climate debate around total emission in US and somehow turn that into geopolitcal leverage is not realistic especially if closer interogation of metric is against most major players interests. I don't think it's splitting hairs rather than acknowleding geopolitical constraints over what's workable and what's not, even if what's workable is suboptimal.
