>>274772049
Yeah. Presumably you could use the gravity gun to [spoiler]just slot the orbs in instead of using the cannons,[/spoiler] but then the level would just end. And that's like 3-4 playthroughs worth of ammo.
It's neat that it teases the gravity gun a bit,[spoiler] but it's a huge disappointment when you finally get it,[/spoiler] at least in story mode.