You are of course right that it's not a monopoly by the official definition. BFC is more like some small restaurant that trusts nobody will ever be able to work out the recipe for their secret sauce. Until then, it doesn't matter if the menu never changes, food doesn't arrive on time, the waiter is grumpy, etc. The moment somebody does figure out the recipe, suddenly the tables are empty.
I used to play a lot of the Close Combat games. When I found Combat Mission, I now can't really imagine going back and playing a top-down 2D game like that again. This could also happen with Combat Mission. All it would take would be some other small company to do a tactical scale WW2 game and bring the engine and tech up to modern standards.