I still think the negative connotation is unhelpful. But primarily it is because you'll never get a listen out of someone like Tettleton. The key to a truly compelling essay is to draw everyone in, even if they strongly disagree, by recognizing that there are other sides to the story .... then BANG! you nail them with the kicker.
I know that there is a vibrant community of TC haters out there, but he's trying to make an argument against what you are saying, and he's doing it by providing data to back it up. You may disagree with his position, but you should recognize that there are many people out there who agree, in whole or in part, with what he is saying, and in an ideal world you would have a response to it that is based in a solid argument.
I think the following are ways to avoid that confrontation, especially if you have limited space within which to write you essay:
1) Make an extremely specific thesis, and do not stray from it. Do not generalize - you MUST be specific. No wasted words.
2) Be very clear about exactly how you are using vocabulary. As I have mentioned by harping on the word "decline" is that it has a negative connotation that is not necessarily consistent with the message you are trying to get across. So either change the word or make explicit how you are using it. (IMO you should change the word).
3) More to the specific argument: American "exceptionalism" as you describe is was brought about by the unique combination of characteristics that made America a world power - a vibrant democracy, accountability, rule of law, robust private business environment, and a will to succeed. If America is becoming less "exceptional" in that regard - i.e. other countries are succeeding primarily through many of those same approaches - then it should be applauded and encouraged. The idea that the rise of other nations will lead to a sort of "landed elite" jumped one more step than I could catch. I would have thought that with more real seats at the table, there would be less of the sort of "elitist" behavior you discuss. It is an interesting discussion (perhaps on another forum) about whether that is a good thing or a bad thing ...