The seed phrase is the weakest link

Key material that a human must store is a storage problem dressed as a cryptography problem, and storage problems are won or lost on boring physical questions.

Failure modes, ranked

Loss beats theft. People lose their backups far more often than anyone steals them — house moves, water damage, a drawer cleared out by someone being helpful.

Design for that first: multiple copies, geographically separated, in a medium that survives heat. Then, and only then, worry about the person who might find one.