OK, I think the problem was that your original post was much too strongly worded. It sounded like you thought that there was no role at all for 256-color and RGB ASCII escape color sequences. But that's clearly not true: just look at a terminal application like bat (a syntax-highlighting cat replacement), which is very popular, and uses sublime color themes most of which use hardcoded colors. In fact, nowadays, when I use the terminal applications that I use most frequently, I make use of their 256-color and full RGB capabilities. But, nevertheless, all the applications I have in mind allow the user to escape hardcoded colors and use the 16 color palette to be used.

But, they do not default to 16-color palette: for example, bat's default theme is Monokai Extended (https://github.com/jonschlinkert/sublime-monokai-extended).

So, as politely as possible, I do suggest that you should get off your high horse; yes people recognize the importance of supporting the 16-color palette but no, it's not some sort of obviously evil abomination to support and even default to hardcoded 256-colors and RGB colors. Quite to the contrary, there are several use cases among modern, popular, terminal applications. They involve color-rich scenarios such as syntax highlighting.

Don't get me wrong though, we're largely in agreement. I wouldn't want a normal terminal app to hard-code, say, a yellow color, which is only visible to users of dark terminal backgrounds, but hopeless on a white background.