All languages are complex in their own way. By surveying and studying the phonetic, syntactic, morphological, organizational factors of languages, one can observe that languages are complex in their own way. One language may have fewer possible consonants, which causes it to have much longer words, while another language may have over 1200 possible consonants due to its possible tones and sounds, giving it words with fewer syllables. For example, Mandarin Chinese has a relatively simple grammar that lacks plural markings or verb tenses, but it also has complex pronunciation due to its four tones.
(Complex, at least, from the point of view of non-tonal languages like English and Spanish. Around 70% of the world's languages are tonal.
Even if linguists find a way to objectively measure linguistic complexity, they must take such measurements from one language’s point of view. Linguistic complexity may include many more forms of meaning, such as whistles or songs that a linguist may misunderstand because they come from a certain linguistic point of view.
Since there are several unknown factors to measuring linguistic complexity, it is better to assume all languages are complex and uniquely structured in their own way, just as all humans and cultures are unique.