A good defensive team will absolutely lock down that first checkpoint. The map requires coordination and communication for the attackers, it's as simple as that.
Personally, I love sneaking in as Genji through the "window" on the upper left side of the entry way, I dash out of range from any turrets/bastions, go around back of the checkpoint and report what I see to teammates. From there, we adapt. Junkrats and Farrah's are super useful to eliminate turrets/bastions, which are always holed up there, especially in the room to the right of entrance.
As genji there's 2 or 3 healthpacks right in the vicinity of the point, so I harass/heal and get a few kills from the back while the team pushes in from the front.