It is considered self-evident that a culture which is “literate”, that is, that has a system of writing which is widely known and used, is more “advanced”, more intellectual, more modern and basically better, than a culture with no writing system. The alphabetic system has the great advantage of being relatively easy to learn. But it’s purpose is probably political and commercial, not intellectual. Letters were written to give orders and instructions. Or at least that is the reason that Empires have expended great effort and cost to provide a mail service.
Certain Australian indigenous cultures had and have and will have complex multilayered linguistic systems and these linguistic systems probably existed in all or many indigenous “illiterate” cultures around the world. Australian indigenous languages are grammatically complex, if that is a meaningful phrase. But other layers of linguistic systems are equally complex. Firstly, let's mention the “mother-in-law” language which is a type of “respectful” language system used when speaking to certain relatives. Then there are the systems of sign language which could be used when hunting, communicating at a distance, or speaking respectfully in some circumstances (such as during a mourning period). These sign languages are also grammatically complex. In a informal pidgin in Australia these languages were called “finger talk” .
But many indigenous people were also multilingual, speaking neighbouring group languages. Often neighbouring groups were named by a particular word in their language such as the “wira-dhuri” - the people who use the word “wira” to mean “no”.
Stories were owned by people, but not just one person. And multiple ownership of a story meant that the stories could be cross-checked over many thousands of years and thousands of kilometers. This is why people had historical knowledge of extinct species of animals such as the “genyornis” giant emu and others, as well as having knowledge of ice-age submarine geography, such as the (submerged) path of the Yarra river underneath Port Philip Bay near Melbourne, Australia.
People made complex four-handed cats cradles with string which may have also had a linguistic purpose, and they used signs drawn in the sand to accompany spoken stories. The signs painted onto human bodies during ceremonies were also linguistic to some extent. Communication could also be achieved through form and colours of smoke and this system may also have been complex and grammatical.
Regarding these multilayered mulitlingual systems, it is hard to think of these societies as “un-intellectual”.