That's exactly the conflating factor that worries me. We know Omicron is much better at evading prior immunity, so we should expect a higher proportion of peopl

That's exactly the conflating factor that worries me. We know Omicron is much better at evading prior immunity, so we should expect a higher proportion of people with prior immunity among Omicron infections, which (all other things being equal) will make Omicron look less severe. But this would be illusory - the absolute number of severe infections wouldn't be less, they would just be diluted by mild infections that otherwise wouldn't have happened at all.