I submitted https://english.stackexchange.com/q/494623/334589 here before it got migrated, but What is the origin and history of the term "grand theft auto"? has remained? Clarification appreciated - thanks!
In principle, a question about "etymology" could be marginally on-topic for LSE, depending on how it is asked. For instance, "consideration" as a technical term developed within English from a verb meaning "mediate on". The legal core of the question would be about the development of the legal doctrine, so to the extent that it is on-topic to ask how "consideration" became a requirement of contracts, such an etymology question would be on topic and has a narrower focus (the earliest development of the concept and antecedent concepts, where terminology is a by-product of creating a new concept). That is not what one gets in the answer to the GTA question or the "sound" question, instead you get guesses or answers that don't actually answer the question. (Similar problems arise with questions about "cross" and "direct" examination, or "replevin" and its relation to "replevir").
On the other hand, a question which in essence asks why English has the words "grand, gross, petty" used in a legal context is a language-trivia question best not asked here. If you don't know about the influence of French on English especially in the context of law, you might be a bit confused if for example you think that "gross" only means "disgusting".
My objection to the GTA question is that it does not establish that "Grand theft auto" is or was a real legal term. In Washington, it is not; nor is it in California. In California, there is a defined crime "grand theft" but that is far as official nomenclature goes. There are complex conditions regarding particular things and values from which one might conclude that there is such a thing as "grand theft avocado", "grand theft mollusk" or "grand theft firearm". It is imaginable that at some earlier point in the history of the California statute, there actually was an offense named "grand theft auto". There has not been a crime "grand theft" in Washington for at least 45 years, and possibly there never has been one. There is a possible legal-trivia question that could replace the GTA question, namely "Does any jurisdiction define the crime 'grand theft auto', using exactly those words and punctuation?".
Depends on the question
Many words in common English usage have very specific and often quite different meanings when used in a legal context. Largely this is to do with the fact that the law requires more precision than common usage and, once a term acquires such legal precision it becomes 'frozen' in meaning within the law but continues to change its meaning 'in the wild'.
As such, questions focused on the legal meaning of words is on topic if they are different from common usage and belongs on English stack if they are not different in a legal context. Similarly, etymology can be useful in so far as it explains the legal thinking behind the development of the word.