Ok. First of all some clarifications :

The Asuras, became the evil spirits, while the Devas, the good.

This is a modern interpretation of the word Asura. Asura as it is used in Puranas and as used in Vedic times is different.

So, the "beings" and their etymologies can be listed as follows :

1. Adityas : sons of Aditi, which means infinite. Adityas are solar deities. 7 and 1/2 (Half-Martand {broken egg}) originally in Vedas, then became 12. Dwadash aditya.

2. Daityas : sons of Diti, which means bound. Daityas two Hiranyaksh, Hirankashipu. Then followed Prahlada, Virochana, Vairochana Bali (maybe Vairochana Buddha). Their guru was Shukra (Kavi Ushana {Kay Kavus}).

3. Daanvas - sons of Danu.

4. Nagas - sons of Kadru.

5. Rakshashas - maternal side of Ravana. Perhaps just violent people, like Yatudhanas (Iranian Yatus).

Unlike the above, Asura is not a race, it is an epithet for gods or mythological entities.

Sura technically means rhythm, and asura means out of it. Asura hence is used to descibe the wild part of the cosmos. Asura could be used to describe state of a god like Agni, Indra, Varuna, Mitra, Aryama etc. Asura is used a lot of times (83 times AFAIK). A lot of Asura mention comes from 3 Mandala 55 Sukta of Rig Veda.

Sura is a rare term (in Avestan Gathas, it is used only for Indra) . In Vedas too it is used rarely. So, we have no record of opposite of Asura being used for gods.

Devas on the other hand, comes from the word root Div, which means daylight. Dyaus was the primary sky god {with Prithvi}, which was morphed into an epithet of Indra. { Dyaus Pitar - Zeus / Jupiter }

Iranians continued with Asura usage, and kept Asura Mazda {perhaps an epithet of Varuna } as primary god. They also kept the dual of Varuna, i.e. Mithra as a prime Asura and continued writing Yashts in his name. Agni/Atar too remained important. Aryama, Apam-Napat, Nasatya all remained praiseworthy in Iranian texts too. Even, Indra with the name of Verethraghana { Vrtraghan- slayer of Vritra} was praised as a mighty hero/asura.

However, they created a class called Daevas and devoted a separate text called Vi-daevo-data {Vendidad} . There they took on Indra and Ahriman {Angra Mainyu, which was the chief evil in charge opposite to Ahura Mazda }. There they also bashed Yatus. But Vendidad as I read it, was more a text to show the dichotomy of good and evil, that is why Neitschze named Zarathustra as his primary character. The main thesis of Neitschze was to rise above the dichotomy {Beyond Good and Evil}.

Eventually, it was Zurvan {time} in which the balance of the two sides was found. But Zurvanism didn't take take enough root in Persia.

Now we come to the part of Indian mythology and how did we end up create Asuras as the bad guys.

The original bad guys { apart from Ahi Vrtra, Namuci} in Vedas were Panis. These were the guys who dwelled in the underworld. Sarama { Hermes cognate} used to go to underworld and come back to Devas to tell them the whereabouts of the cows they had stolen from Devas.

Other pantheons descended from the Proto-Indo-Europeans don't seem to have the same dichotomy

These Panis are the cognate of Vanir in Aesir/Vanir conflict of Nordic myth. Even today the word for commerce, Vanijya (or Baniya) is explained to come from Panis. In modern usage, however, the abode of Panis is called Pitriloka or Yamaloka or Vaivasvata loka. {Southern Celestial Hemisphere}

Aesir, the older gods and Vanir the new gods (and before that Giants{Ymir} and Aesir). Titans the old gods, Gods the new Gods in Hellenic myth. Marduk killing the Tiamat. --> All mature mythologies have these two waves of gods.

One wave is a class of giant, wild, savage, superpowerful gods with no leash.

Second wave is a class of more humane, relatable immortal deities of complex characters.

Even the monotheistic desert cults had their old Gods like Jewish Baal, which they converted to Beelzebub {one of the devils}. Similarly, Tawuz Malek of Kurds got a rough deal by becoming the chief devil, after introduction of monotheistic god. Pan, {Perkunos - Vedic Pushan, the god of forest and everything} was converted to Devil himself. Why the devil is a goat-head in Christianity, because the lovely god Pan was a goat-head.

So. Conclusion

In comparative mythology, we observe that a culture generally has two layers of deities, the old and the new, which at some point are in tussle with each other. Their tussle is the primary symbol battle of wild and civilized. Most beautifully depicted in the story of Samudra Manthan, where all sorts of gems and poison comes out as a result of this tussle.

The first battle which the gods win, perhaps depict the victory of man over the wild.

The later battle is an every-continuing one, which only leads to a balance.

A culture may experience multiple waves of gods and pantheons, this could happen as a result of many things {empires falling, kings changing etc.} However, it has been noticed that tropical/coastal climates suit polytheism. meanwhile, deserts could rapidly go into monotheism. IMO, Zoroastrianism could be explained more by geography, and less by theology.