Omicron is milder by 'design'. A mild case of say Delta means that it hasn't expanded it's population enough before the immune system starts to deal with it. A severe case of Omicron will still produce mild symptoms for the most part.The only downside of mild/asymptomatic infection, from what I hear, is that it might not engender as strong an immune response as a more moderate or severe case of COVID would. Now, I'm not sure if that's completely true, since they seem to be referring strictly to circulating antibody titers, and it stands to reason that if there is less of the virus to clear (viral load has always been correlated with severity of infection), fewer antibodies would need to be marshalled to combat it. I'd love to see a T/B cell analysis for mild/asymptomatic cases versus more severe cases 6 months post-infection.
I also wonder what this pattern entails for immunity conferred by Omicron, which by all accounts produces more mild disease. You have some folks saying that Omicron-induced immunity confers protection against Omi plus all previous variants and possibly against future variants (in a similar but more pronounced manner as previous COVID infection with, say, Alpha or Beta provided protection against Delta etc.). But then you have the train of thought noted previously: that milder disease yields less robust immunity. I'm waiting to see some real studies/analysis on the specifics of the immunity produced by Omicron infection.