how can something that costs 8 to play and 3 to activate the ability ever be flexible?
The reason is because to put Anubis in a deck, you need time and aether. To put turquoise nymph in a deck, you just need aether. So you could, in theory, make, say, an aether/life deck and quint your frogs, without anubis, or make an aether/water deck and quint mind flayer. Anubis is more limited in the decks it is useful in, but in the decks it is useful in, it's better. Anubis is stronger but less flexible, and turquoise nymph is weaker but more flexible.