nothing can cut through serpent trans once its up but here is the problem. If an enemy begins his combo before you cast it it will be like you missed the cast rendering it ineffective. This is a flaw in the spell itself\ and a major reason many veteran tos opted to stop using it. 5 min cd and a 50% chance you'll fail casting it make it a pretty useless spell to someone like me but as you said im pvp 10 i can take a beating. you cant as of yet. This is why i say use it pre-emtively instead of defensively. I found when doing that before it worked very well.
Fangs offers a single target a 90% miss chance meaning there is still a 10 % hit chance so its not 100% no but it is still highly effective to thwarting melee attacks. Donot disregard this one so easily.
the thing about melee combos is once theyre finished and they land it doesnt matter if you bubble or line of sight the damage is done.