I believe I already said I accepted that as a valid argument.

It's ipso facto evidence it will cost the US more than a hypothetical other signatory power which has the exact same targets, or less ambitious ones, while lacking such enforcement mechanisms. Beyond that, you're out of 'ipso facto' territory and into 'how far do we estimate this other country will get' territory. You'd need to first see which other countries have more ambitious targets than the US, and then estimate to which extent they're likely to achieve their goals considering their greater leeway to fall short.

I'm denying that 'doesn't have to cut emissions until 2030' means 'doesn't have to do jack until 2030' as you keep suggesting. As I was saying to RT, China is a country that's growing massively, largely through heavy industry. It's pretty obvious mathematics that if your emissions are currently growing at a rate like China's, the effort required to get them to actually reduce by a given percentage is massively larger than the same reduction would be for more developed nations where emissions are stable or already dropping. So that point of their emissions continuing to grow doesn't mean much without serious analysis of the numbers.

Now, your new links now do provide some of those numbers to argue that China's pledges were pretty unambitious even so, so that's a lot more convincing. And you're right that a fair comparison should take into account the efforts already made before the Paris Agreement as well.