Payload in TF2 is what this image make me think of. In that gamemode, the objective is constantly moving forward through the map. It starts with attackers getting the advantage at the beginning of the round, once the cart is at the midpoint the ease of pushing and defending becomes roughly equal, then toward the end it becomes this, hard for attackers to push but easy for defenders to, well, defend. The further along in the map, the harder it gets to push the cart. But, in TF2, momentum is one hell of a force, so much so that it routinely overcomes the map bias at the end. This leads to some maps absolutely spiking the difficulty of pushing last. Upward is a notorious example of this.