Aren't game engines like Unity and Unreal only appropriate for first person shooters or third person adventure games? What about 2d platform games? Real time and turn based strategy games? Flight sims? Sports games? Board game remakes? You wouldn't choose a generic "game engine" for any of these, would you? Honest question, I'm not a game programmer, but as a programmer it sounds unlikely that a single package could be appropriate for so many different genres of games.