Venom eats morluns brains , morlun only get's stronger because he absorbs spideys 'animal totem' crap . (you know the bull the writers pulled out of their asses about him being 'magical' ) Venom has no 'totem spirirt' . Instead he has a violently insane symbiote with a hankering for brains.
Again, he was only stronger then spidey because every time he touched him he drained spideys 'totem animal spirirt' . It took spidey injecting himself with radioactive liquid (WTF, why the hell didn't he die from cancer anyway ?) to take out morlun.
^ The ability not to die from the radiation proved that he wasn't a true totem. Morlun isn't as strong as Thor. Since he drains life force from those he hits, it seems to hit harder. However, Venom wouldn't be as hurt by it.