Fair point.
But, actually, you can just run it with no config files and it will work. Then you can say for example "hmm I wish the background was black and font white," and google around for the best config file candidate to add that, and boom. And slowly build up.
It's a thing designed for xorg directly, which itself isn't meant to be used directly. So there are many different ways in which it can be integrated, which can produce something of a duanting maze of options.
In my case, for example, I have a very simple window manager. I thus have a .Xresources file in my home directory, with maybe 3 lines that don't even reference xterm directly, but they determine a color scheme that ends up affecting xterm's behaviour.
One of those few cases where random tips and tricks from google will help you more than the man page.
In fact, if I think about it, I may have 3 or 4 config files, none of which are xterm config files, where xterm's behavious is modified. It is meant to work through your xorg setup, not along side it.