This is just false. Engineering is still about taking small parts you understand entirely and using simple techniques to compose them into larger things you want. Sussman's justification is an abject surrender to shitty complexity. Engineers need to develop a taste for simplicity and elegance, especially at the beginning of their education.
Incidentally, an overlooked advantage of teaching in Scheme is that it levels the playing field, as pre-undergrad programming classes almost never use functional languages.