To be worth a damn as a designer, you need to know three key things: who you're writing for, what has worked for them in the past, and what has failed them in the past. You seem to be uncertain on the first, and clearly avoiding learning the other two.
What works for you and your group is almost immaterial. To succeed, you need to know your target audience. You also need to market to them. Don't waste money marketing to others, get your ads targeted. You also need to listen to them, too.
Internal playtesting, likewise, isn't that valuable. You'll learn 10x more by handing an unfamiliar with it GM the game, and watching them run it for equally new to it players — and keep your yap shut while they do. You'll see what they struggle with more that way.