I don't think it's hyperbolic. If someone has sent you an email in plain text with wrapped lines, your mail client will know this and it would be reasonable to assume that perhaps the sender may be using a mail client not capable of rendering HTML emails nor autowrapping long lines. It would be a sensible choice to format the reply in the same format as that of the email received.

By stating "HTML email has features that most people actually want. The world has moved on...", you seem to be implying that the primary method of communication of Linux kernel developers is irrelevant and their use-case for email is not important. In fact, the more I think about this, this is a classic example of Embrace, Extend, Extinguish.