Firstly, the Qur'an wasn't written by the Prophet, he would dictate it and it would be written by his scribes.
Secondly, it's hard to argue that Islam has had a negative effect on Arabic or caused it to lag behind. In fact, it's easy to argue for the opposite. It's a historical fact that the Arabic language developed and proliferated rapidly due to the rise and spread of Islam. This is when its script and grammar were standardized, and when more and more works started being composed. And shortly thereafter the Islamic Golden Age began.
I don't have any issue with Hebrew, and maybe it is easier to learn. But this is because it was a dead language which was revived, resulting in a simplified language. Almost every other major language on Earth will have the same amount of "innovation" as Arabic. In fact, Arabic has many colloquial dialects which are used in day to day conversations, and these do consist of a simplified version with many loanwords. So I really don't know what you mean by a lack of innovation.