Is there any advantage to use doctrine:mapping:convert with --from-database option in favor of doctrine:mapping:import in this use case?

Good point. I just followed the guide and this fixed it for me, but I just tried this way and it works fine. Maybe it still can be added to the guide, because I wasted some time on it and so could others..
Commands used:
php app/console doctrine:mapping:import --force --em=default AcmeBlogBundle yml
php app/console doctrine:generate:entities AcmeBlogBundle --no-backup

You're absolutely right. The guide as it is does not work. I assume we can replace doctrine:mapping:convert with doctrine:mapping:import. I'll dig a bit into this issue and create a pull request for this.

Nonetheless, feedback whether or not this is a good idea is really appreciated.