After playing this mastery for a while I've come to a conclusion that it has one big flaw that is setting it back as a mastery.
The biggest issue I see with it is that for a mastery that does most of it's damage with melees, it's melee damage is insanely low.
After all the changes it got the kit is in a really solid place but it's melee just does too low damage and it's what you use the most in combos and fights.
I think that the mastery should get at least one more pipe in the 50+ level range that has better damage and that the lvl 35 Seathorn Pipe needs slight number tweaks. Seathorn Pipe (current stats) - 11 base damage, Poison II (6 dmg for 4 ticks) = 35 damage after DoT ticks
The issue I see with this is that the base damage of the pipe has not improved at all from it's lvl 10 pipe. The DoT it has does nice damage but it takes time for DoT to tick so for Bubble which relies on doing combos it doesn't really help much cause the base damage is the same.
How it could be improved:
1) 27 base damage, Snake Poison (2 dmg for 4 ticks) = 35 damage after DoT ticks
2) 19 base damage, Poison I (4 dmg for 4 ticks) = 35 damage after DoT ticks
Basically the DoT of the pipe should be weaker in damage but the base damage of the pipe should go up. The total damage the pipe does stays the same.