Adi Shankaracharya once said to the Hindu Brahmins “Grammar won’t give you enlightenment”. The brahmins in their obsession with understanding each and every word of the vedas spent all the time reading and understanding and no time practicing.
The same is happening in Buddhism, the path of Buddha is not a easy one Shariputra did not get praise from Buddha for his grammar but his practice, Venerable Punna only took the teachings in short worked hard and liberated himself.
I don’t think anyone thinks that grammar alone will get you enlightened. I’m curious, why would you think that?
What gets you enlightened is the eightfold path. Now, the first factor of the eightfold path is right view. Right view is brought about by two things: the teachings of another and one’s own inner reflection. As far as the teachings of another go, the very best is the word of the Buddha. This is contained in the body of texts we call the EBTs, the Early Buddhist Texts.
The EBTs are a large body of texts in Pali, Chinese, Sanskrit, and Tibetan. There are translations of some of these, and for most people the translations are fine. But for those of us who love the teachings and want to learn more, we need to look at the original texts. That means learning the languages, including grammar.
So: grammar helps you understand the Buddha’s words. The Buddha’s words support your right view. Right view is the foundation of the eightfold path. And the eightfold path is what gets you enlightened.
On the other hand, if you discourage people from learning the EBTs, you’re discouraging them from learning the Buddha’s words. If you discourage them from learning the Buddha’s words, you discourage them from improving right view, developing the eightfold path, and realizing enlightenment. That means you’re making an obstacle to your own enlightenment and that of others.