So I been reading it and I came to the realization, I might be missing something. However does your companion never gain the mythic dying rules? On top of that it dsoesn't make your companion more tanky, it is already difficult to keep an Animal Companion alive at higher levels so not including bonus Hit Points and the same Mythic Dying rules seems like it'd hurt the Beast Lord for both mechancis and rp flavor when their Mythic hunting hound dies.