It's not up to me to account for party member interaction. It's up to me to make the class stand on its own just fine. The barbarian's animal companion does not have the Share Spells feature that the druid's animal companion does, making it vastly weaker for teamwork abilities. Additionally, the barbarian may only select from a handful of creatures (and the rest of his class features are based on them too, so he might take a weaker creature like a snake so he can get Snake Totem features)The other slight worry I share with a previous poster: the animal companion. I think it might be too strong. This could be made worse in a party with a druid and a barbarian, with the druid buffing both animal companions. I have few alternatives ready if you insist on having a lion available at level 6 though. Possibly you could reduce the high level problems by making your druid level half your barbarian level +6 instead. That, or design a lesser lion to fill this gap.
The barbarian's animal companion should certainly not be weaker than a druid's, as you suggested. The barbarian class is so inferior to the druid class in pretty much every way that his pet shouldn't suffer for it.
To reassure you, though, I based this class feature on the Totem Druid variant animal companion (Dragon Magazine something or other), which the totem druid gets at level 1 and gives him a +3 bonus to his AC level as well, though he may only select his totem animal as a companion.
AbsolutelyWould I be allowed to use this in my campaign setting (Blades of Keran) NeoSeraphi?