Couple things. Dropping the symbiote might get Venom through the sonic shield, but the laser light sheild disintegrates matter. That shield that he forced his way through before fighting Wolverine? That was just electro-shocking him. flesh disintegrating shield >> electro-shocking field. I'm pretty sure it counts as a win if the flesh has been melted off the front of your opponent's body.
Also, Long is right. Her powers carry an immunity to damaging light
and sound. Touching her own forecefield won't hurt her.
Honestly though, I'm not leaning towards either. I do think it's kinda f*cked up that Venom can work through his two vulnerabilities like that, but a scream that can shatter/liquefy steel beams should still do some damage, since durability is limited to under Cage level. Still, I haven't seen an utterly convincing argument for the forecefield(s) keeping particles-o-Venom out.