> Unity and Unreal are absolute powerhouses if you have an actual idea and a burning desire to express it as quickly as possible to as many customers as possible.

If your game idea fits well into the structure of these engines: perhaps.

But I can tell you that lot of ideas that I have for games ("games" is to be understood in a somewhat more broader sense) don't fit these structures well. So I am very certain that for the game ideas that I have in mind, writing an own game engine would very likely be the better choice.