actually, nagas are better than djinn in the first stage with full tactics; they can reach the enemy quickly. In the second stage, they don't give up. In the third stage, they attack in large numbers.

Yes, maybe that's true; I don't deny it. BUT (as always, there's a BUT in any situation), they still need to reach the heart of the enemy, and they'll be shot down. You can use teleportation, but then the naga will be in trouble herself – everyone will come to her, and that's it for her. A djinn is better in this regard – it's a ranged attacker, a mage, and always protected by someone (IMHO). Although it also has its drawbacks – mana can run out, and then it's over! In general, it depends on the situation, but it's usually better to take djinn.
This is just my IMHO!