I wrote in my parent comment that this was based on personal observation. There is no such thing as conventional wisdom on such topics, there are just widespread opinions:
Note, there are two points we are discussing here:
1. Is there a way of saying that some grammar is more complex that others - objectively?
2. Does writing influence the complexity of the grammar?
Now, for both cases, I base my opinion of observation, and not off any scientific papers. Since you are doing the same, the only way we can settle this duel is by trying to show as many examples one way or the other to resolve the issues.
Regarding the first question, I'll just assume that we both accept that there is difference in complexity in grammar between languages. Or do you not think so?
Regarding the second question, I'll say this:
* Chinese Grammar is simple, but it's very clear that Chinese style writing cannot have the same influence. If you do not know a chinese word, you cannot write it, and you cannot read it. As such, you are not likely to use it, and the word will tend to die. In western style writing, you can attempt to write a word from having heard it once. It's also much easier for words to live on, because words are easily copied.
* Unwritten Creole and Pidgin Languages always do very similar things to western languages - they strip it of certain grammatical constructs, and it ends up being like most unwritten languages - past tense and future tense are created by adding words, and not by changing words.
Ignoring everything else, I wanted to answer this one:
> 1. Is there a way of saying that some grammar is more complex that others - objectively?
I think so. English verbs, for instance, are significantly easier to conjugate than most other European languages. There's just less stuff to remember.
Another example with verbs is the subjunctive, which has all but disappeared from English (I wish I were, rather than I wish I was), but is still very much required in a language like Italian, even in the present tense: (Credo che sia importante instead of credo che e` importante, which is translated as "I believe it's important").
When you take complexity out of one part of a natural language, it ends up sneaking back in to another part.
English verbs by themselves are easy to conjugate, but English also uses a large number of modal verbs (I did write, he is hacking, we used to travel, she had better shut up) that these other languages lack. So while a native English speaker learning Spanish has to learn a lot of verb conjugations, a native Spanish speaker learning English has to learn a lot of modal verbs, and the special rules for conjugating verb phrases that contain them.
Note, there are two points we are discussing here:
1. Is there a way of saying that some grammar is more complex that others - objectively?
2. Does writing influence the complexity of the grammar?
Now, for both cases, I base my opinion of observation, and not off any scientific papers. Since you are doing the same, the only way we can settle this duel is by trying to show as many examples one way or the other to resolve the issues.
Regarding the first question, I'll just assume that we both accept that there is difference in complexity in grammar between languages. Or do you not think so?
Regarding the second question, I'll say this:
* Chinese Grammar is simple, but it's very clear that Chinese style writing cannot have the same influence. If you do not know a chinese word, you cannot write it, and you cannot read it. As such, you are not likely to use it, and the word will tend to die. In western style writing, you can attempt to write a word from having heard it once. It's also much easier for words to live on, because words are easily copied.
* Unwritten Creole and Pidgin Languages always do very similar things to western languages - they strip it of certain grammatical constructs, and it ends up being like most unwritten languages - past tense and future tense are created by adding words, and not by changing words.