I still think a non-gamer perspective during the rules development and book organization/layout process is valuable, even if the primary audience is existing wargamers and the main intent isn't to get non-gamers into the hobby. If the rules are unclear or overly brief in explaining certain concepts and the reader has to draw on prior experience with DBx/Black Powder/Lion Rampant/40k/whatever to understand what the author is going for, then that's poor writing. An outsider or beginner can show the author where things need to be highlighted, clarified, or reorganized to get across the intent of the rules.
Again, this is not really a case of including a "what is miniature wargaming" section and a glossy model showcase/painting guide in the middle. But if something like initiative is a core element of the game, don't just write 'dice for initiative' somewhere in the turn sequence and then explain what that means at some later point without really flagging it. Sometimes that stuff gets sort of buried or glossed over because the author maybe implicitly expects the reader to be familiar with how it works in a similar game, or because he/she's spent so much time working on the rules that it's hard to get into the headspace of someone who is new to the game and so takes key concepts for granted.