Most seasonal flu I've lived through, I've never seen everyone in the household come down with it immediately at the same time. In my home everyone came down with covid, kids and adults, almost exactly at the same time with the same symptoms.
Omicron can be 0.1 times as lethal as delta, but if it spreads to 20 times as many people as delta it will still be twice as deadly.
Clearly we don't have enough information right now to do the calculus, it looks like omicron is less severe, it looks like it's more contagious, but how exactly this balances out seems to be unknown. Though I have seen more hospitals in my region reporting record admissions.
I'm still seeing bars in the area sending out email campaigns encouraging people to come up and party for NYE. It's funny that while requiring vaccines they make no mention of "stay home if you feel sick". Right now I don't think we have enough information to correctly assess the real risk of actively encourage people to gather for NYE, but given what we do know it certainly seems like a risky idea.
edit: I'll add the "as low as" phrasing is a bit odd, since my understanding of past variants is that their risk to children was lower than the flu. This means that, relative to other variants, being "as serious as the flu" would be an upgrade in the level of risk.