The most useful monster.

It's a waste to dismiss Nagas like that; they have a decent attack and good combat stats.
Djinn are certainly useful, but their mana is limited, and they aren't very helpful in the final battles either; their range of abilities is limited.

The only downside of Nagas is that they are expensive to build.

Well, maybe in places where mages are already leveled up, and there's no need for Djinn, Nagas might be more useful – I won't argue that with a good buff, they can become powerful.
But in the early stages of the game, Djinn are much more useful.

Even if we take an equal number of Djinn and Nagas and put them head-to-head, then...:smile15:
The Nagas will simply not reach the Djinn and will fall somewhere in the middle of the field, and no Djinn will die. The same situation applies to any other neutral creatures – in the early stages of the game, Djinn are decisive.
And then we'll get to Titans, we'll see.