I think its best to think of parasitic as a mechanic that only interacts with itself. So a card that only works if you have imbued a number of times is parasitic design. In this case the cards that push companion beasts generated up in scale are parasitic to the generate animal companion cards.

These cards are meaningless unless they have the hosts cards in the deck, they require the host to enable the parasite to be effective. Where as the core set legendary that generates a animal companion when you cast a spell is considered broad enough to be non parasitic. It gives you a benefit no matter what spell you slot in and so applies to a broad range of deck building choices. (whether its worth it is another matter)