Ahh! to feat Fangs of Set, you need 35 points in Lightning tree.
That means you are losing 13 points on Thunder tree.
To lose 13 points in Thunder tree based on spec on this main post, that means not only you are losing Vital Shock, you are also losing Vitality of Set (that gives you %12.5 crit and %10 Vitalizing Jolt) and you are also losing Aura of Nebthu.
That's too much DPS to give up for Fang of Set, that is not even a 100% bubble!