While human evolution is not predictive, it has selected for a wide variety of survival-associated adaptations beyond the mere individual.
Humans had life expectancy even shorter than our fertility period until recently and they developed as social species hundreds of thousands years ago, for which living beyond fertility period is beneficial (grandparents were invented by evolution too).
> And bear in mind that most people don't have a problem surviving colds
That’s modern people with access to antibiotics etc.
> that was probably more true for much of our evolutionary history when we were living much more isolated lives, and not cohabiting with chickens and pigs
For much of our evolutionary history people were eating animals, getting viruses with them.
Antibiotics don't help against viruses like colds. And we live a life that is has a higher degree of social connectivity than our ancestors, allowing for faster spreading of disease, so we're arguably worse off.
Yes. But they help fighting secondary infections, which are common.