And if those people under 70 were exposed gradually to the virus, they'd survive in higher rates than the vaccine? So would it be more effective to expose them to the virus instead?
By "expose somebody gradually to the virus" you're describing certain vaccine technologies.
Live viruses have a nasty habit of reproducing, spreading uncontrollably and killing a lot of people along the way. The people who survive do gain an immune response though.
Some virus technologies use "live-attenuated" vaccine, which are weakened (but living) versions of the virus which promote an immune response without causing illness.
The vaccine doesn't kill you in the cases where it doesn't work.
If you are in the group with 0.5% chance of death without the vaccine, then with a 95% effective vaccine, you would have a 95% chance of being immune (0% chance of dying from the virus) and 5% chance of having the normal 0.5% chance of dying.
No, the virus can kill and cause long term problems to people under 70, at a rate that would be unacceptable for any vaccine.
It could be a last resort solution if we had no hope of an effective vaccine, but it looks like the results are quite promising so far, so no need to go to such extremes.
"get people sick in a controlled manner" is a form of vaccination. Just a particularly dangerous kind, because you are using live viruses instead of non-infectious lookalikes. It is like training soldiers by putting them in real gunfights.
