Here's why it's difficult to make such a judgment:
* Every language has its own unique grammar. What might seem "poor" in one language could be a perfectly valid feature in another. For example, some languages have very few verb tenses, while others have a vast array. This doesn't make one language better or worse, just different.
* Grammar is constantly evolving. Languages change over time, and what is considered "poor" grammar today might be perfectly acceptable in the future.
* Grammar is not static. There is a range of variation within any given language. Regional dialects, social groups, and individual speakers all influence the way language is used.
Instead of trying to rank languages by their grammar, it's more helpful to appreciate the diversity and complexity of human languages. Each language has its own unique structure and beauty, and all languages are equally capable of expressing thought and feeling.