There are interesting challenges with data collection (and I don't think the survey paper discussed in the OP really solves this problem), but to be clear, some

There are interesting challenges with data collection (and I don't think the survey paper discussed in the OP really solves this problem), but to be clear, somewhere between 10-30% of Americans average fewer than 6 hours of sleep per night, which increases your risk of catching colds by 450%. So getting less sleep than you need is definitely harmful, the questions become: a) how much do we really need, b) how much are people actually getting, and the jury still seems to be out on both of these.