There were a couple of eaten lasers, cartoon power allowed to reduce the damage, but it was still there. There was a blow to snakeman, during which Luffy grunted in pain, this blow threw him into a wall of lasers, which, according to Luffy, almost killed him. That is, lasers can clearly cause damage to Luffy in 5G. Also, if Luffy didn't take damage during the fight with Kizaru, it doesn't make sense that he passed out to helplessness when after the fight with Lucci he just aged, but was conscious