Advice divergence can as easily reflect our lack of knowledge as actual complexity of the problem.

Certainly. It's something you'd expect to appear either way.

However, if the relationship between akrasia and glucose were the same as the relationship between scurvy and vitamin C, you would expect that the divergent-but-successful self-help advice would all involve ways of (directly or indirectly) modifying glucose availability or depletion, in the same way that all the divergent-but-successful scurvy cures affected vitamin C consumption or depletion. (e.g. fresh meat, short trips, not using copper pots, etc.)