I fully admit I'm too lazy to do serious research of that kind myself, but then that's why I admit to not actually knowing whether the American targets were indeed much more onerous than those of other major nations. You seem very certain that this is the case and even that some countries' economies wouldn't suffer at all, which is good for you but I'm not going to buy it just like that.
It's possible that you're right, but at this point I'm kind of figuring if you had the numbers to prove it, you'd have shared them by now, instead of only arguments like the one about legal culture, which may be valid but doesn't say much until it's combined with an analysis of the numbers.
Not that there is a single way of objectively determining if the burden is fairly spread. The best kind of data to compare would probably be something like the reduction in GDP growth percentage for each country as a direct result of their efforts to cut emissions, but still you could find arguments why that's not fair, and the different time periods and different baseline dates of the pledges make comparison even more complicated. But it would still be better than not using data at all.
So, yeah, up to you if you want to dig deeper and build a serious case. Fine by me to just leave things where they are and both walk away unconvinced.