If the threat is annihilation, well, I guess it depends how advanced Sweden's bio- and chem-engineering is in order to quickly create weapons severe enough to counter a nuclear power.

When your threat model isn't annihilation but simply being overrun and submitting to a new ruler and set of foreign laws and customs, having a population with guns and gun training works pretty well to make it difficult for an outside party to achieve that even with massively better war tech.