It's not like strains of the virus are made by intelligent design. The point is that Omicron became dominant because people due to a lot of factors, its high transmissibility and people's disinterest in quarantining among them. If Omicron 2.0 came out with the same transmissibility, but a notably higher lethality, people's interest in quarantining would have increased significantly, which could have prevented Omicron becoming the dominant strain in spite of its increased transmissibility.