Like you said, Nostr is not a timechain.

Nostr should not be relied on for immutability like a strong Nakamoto consensus blockchain is. Nostr is better suited to paying for off-chain data replication across as many computers as possible, on a gradual timeline with daily/weekly zaps to the nostr nodes hosting the data.⚡️

The synergy comes from them working together, like the other off-chain layers do.