A recent discussion about the evolution/devolution of languages often left me wondering this: When someone says (speaking relatively, of course) that "This language is complex" or "This language is not very complex," what could we possibly be talking about other than grammar?
The possibilities I can think of are: diction, vocabulary, orthography, alphabet/writing system, and pronunciation.
Is, for example, Spanish less complex than Italian based strictly on having a more limited vocabulary? Or is Mandarin Chinese more complex than Italian based strictly on the relative complexity of its graphemes? Does "grammar" trump all when it comes to making such summary comparisons?
My initial answer to this question was "yes, of course it does," but now I am uncertain.

Orthography and alphabet are important only for learning a language. Pronunciation and grammar are the “true complexity”
IMHO orthography and alphabet are important only for learning a language. Pronunciation and grammar are the “core complexity”