We do not have data to support the claim "natural immunity will last many years", as the disease hasn't existed for many years. There are studies that go in both directions as to whether recovery from infection provides better protection against future infection or not, and there seems to be a lot of cherry-picking by people trying to support their own arguments.

If we can't eliminate Covid, there will be mutations that reduce effectiveness of immunity whether obtained by vaccines or by previous infection, and everyone will need boosters, like we do for influenza shots.