I would say that if the game is not based on luck and purely skill, it won't really be a good gambling game as it would result to really good players or experienced ones to be at an advantage and those inexperienced newbies or lesser skilled players to be in a great disadvantage. Take for example, the game of chess. It can't be a gambling game, since what if grand masters play on the game and beat every player there is. Then that means they will take in all the money of everyone.

Let's talk about poker. It is a skill based game, however it still greatly relies on luck of drawing the cards. Yes you can have a probability calculations whether your hand has a great chance of winning, but it will still depend on the draw of the cards if you win or lose. So it is still different from a purely skill based game.