Variants may not evolve to be less dangerous.
Of all the COVID misperceptions, this is the one that seems impossible to kill. So many people assume that COVID will evolve to be less deadly. That's certainly not guaranteed, and it might even be 50/50 for which way it goes.
Delta was a good example. It multiplies much faster in your cells, which causes you to be sicker, but also to spew far more viruses even earlier in the cycle. So it both spreads better and has higher severity. If, hypothetically, Omicron is 3x deadlier but spreads 50% faster, it will absolutely replace Delta, despite killing more hosts.
Long term, our immune systems will get better and better at fighting COVID variants after repeated vaccinations and/or infections, but that's not the same as the virus evolving to be nicer to us.