However, each subsequent re-infection is expected to become milder as people's immune systems get used to the virus and learn how to fight it (as it is the case with common colds)
The vaccine we have is not very effective, the evidence for protection from infection waning is getting quite strong, however it still protects from serious disease in all but the most vulnerable, it's the same with infection, although infection is possibly more protective (although may be only because we only have re-infection data for more serious initial cases) this certainly puts it similar to lots of other respiratory infections of all sorts.
Covid actually is better than many, as unlike some others (like RSV) there is not a time when it's serious for young children. We don't need covid to get milder, we just need vulnerable people protected, either with vaccines and lots of boosters, or infection before they become vulnerable.