I tend to draw a different conclusion from Practiced Spellcaster. After all, Practiced Spellcaster offers nothing to the full-HD spellcaster. If we assume that Natural Bond is meant to fill the same function (bring a class feature from a multiclassed character up to full-HD level,) then why should it provide benefit to the full spellcaster? After all, Practiced Spellcaster, the first precedent-setting feat in this vein, doesn't.
I believe that a FAQ entry for Natural Bond would be different. Caster Level interacts with spellcasting differently than class level interacts with the druid's companion, so simply porting over a ruling isn't going to necessarily be accurate.