You seem to forget damage shields. Probably intentional. :rolleyes:
And, if you believe that this proc (300 dmg/50%) was the reason MAs had that awesome damage than the problem has to be somewhere else.
It's a flat out 25% chance, 624 damage, subject to nano damage modifiers. Returns 81% aka 505 HP, which is subject to heal modifiers.
And only an MA would use the Trader LE life tap procs.
Further more, Probability distribution works a bit different.
Maybe some math genius here can calculate us the chances of proccing any of the three events, but including the fact that two or even three of those events are not possible to happen at the same time.