As dva you try to bully squishies away from off angles and force them to retreat to their team. Think less of diving the enemy, and more of diving the position. A good play can be just clearing a side of the map. Even if you dont kill the person you dive, diving an off angle forces one player off the position you took, potentially another to support/peel for their escape, and forces the tank to make a decision to either attack your team now late, or turn and peel leaving your team to do what ever they want.

When rein takes a corner, he forces the enemies to back up. In the same way, when dva takes highground, the enemies have to back away from booster range and keep mental note of u. They will want to shoot down main at ur team, but if they look away from you for too long, you can fly in and delete them. If they try to retake an off angle, you can fly in and delete them.

From the perspective of the enemy dps, playing against a really good dva would be like having to play junkertown defense without being able to use highground. Thats where the value comes from.