Understanding Quranic Terms: Why Some Sins Are Described Differently

Salam everyone! Hope you're all doing well. As someone whose first language isn't Arabic, I sometimes find it tough to grasp certain Quranic terms on my own-especially since I don't have many Muslim friends nearby to ask for guidance. Really appreciate being able to share questions in spaces like this! Lately, I've come across some Muslims who identify as Quranists, meaning they mostly rely on the Quran and set aside hadiths and tafsir. While that's not my personal approach, it got me curious about their perspective. This Ramadan, while reading Surah Al-Ma'idah (verses 3 and 90), I noticed references to practices involving arrows or similar tools, which I learned are forms of divination-like trying to predict the future or outcomes. Online teachers I've listened to often label this as shirk, but the Quran itself uses the term 'fisq' here. Some Quranists I've spoken with argue that if it were truly shirk, the Quran would clearly state it, since it's Allah's perfect word. This made me wonder: how do scholars explain things that aren't explicitly spelled out in the Quran? I'm not referring to hadith or tafsir-just focusing on the Quranic text itself. If anyone has insights or explanations, I'd love to hear them, as it's come up in discussions I'm having.