I would say that, in general, natives judge your language skills by your WEAKEST language component. "Really nice" is much better than "decent," so if your grammar is currently a bit below "really nice", and your pronunciation is a bit below "decent", most natives would probably describe your language skills as "a bit below decent." You should put more effort into improving your pronunciation than your grammar. By contrast, if your grammar were WORSE than your pronunciation, I would tell you to work on grammar rather than pronunciation.

I would tend to agree with Chris. People expect a language user's skills to be more or less on a par with each other. Here are some ideas about listeners' perceptions of language ability: If someone is clearly a beginner, listeners will be prepared for a low level in all competencies. For example, if a desperate tourist rushes up to you in a station and garbles something like "Paris? Train? Go? Time?" in a dreadful accent (in any language), people will be sympathetic and will try to understand. They'll make allowances for both limited grammar and poor pronunciation and will do their best to help. However, if people are using a language as a lingua franca in a professional context, everyone needs a decent level in all skills. If you have a good level in one skill, listeners will NOT make allowances for shortcomings in another. For example, if a colleague's grammar is at a noticeably lower level than their pronunciation, this will be a source of stress and irritation: people will think "Oh for goodness sake! Why doesn't X ever conjugate verbs properly? She speaks really clearly, so surely she must know it's wrong!" Likewise, if someone's pronunciation is much poorer than their grasp of grammar, this will annoy people, and provoke reactions like "Why doesn't Y bother to say the ends of his words? He writes emails perfectly, so it's not as though he doesn't know the words! You'd think he'd make an effort to say them properly, wouldn't you?".

Chris had an excellent suggestion to work on your weakest area. To answer your question in a general sense, beginners should do extra work on pronunciation. This will improve their listening and speaking at beginning, intermediate, and advanced levels. It will also save the effort of unlearning bad pronunciation (based on the sounds of their first language) and relearning standard pronunciation.

Work on every aspect of your language acquisition. No point is less important than the other, but as language is an art not a science, be happy with all your creative output but don't rest on your laurels, constantly strive to improve.

Both of them play an equally important role in comprehending English language. Without decent pronunciation, nobody would be able to understand you and without proper grammar, people may misunderstand you. So, I think both of them are important while learning English or any other language. Hope it helps. 😊