If you don't know what you're looking for, you're going to have to read through 100 pages of (potentially) terrible handwriting. If you don't even know there's a seed phrase in it, I'd say it could be safer than a piece of paper with 12 words.
yeah but in that case, the person the diary belongs to might forget how to decode it too. so back to square 1. whenever you try and obfuscate information inside other information, you run the risk that you forget the encoding process and how to recover the information.