I checked WoL from last night and my overall Missile Barrage proc rate (3 hours, 8 bosses) was :
Missile Barrage 513 990.4 32.7 %
the Rotface fight even shows MBarr as low as 24.5%
for Val. Dreamwalker it is 26.2%
generally, it's in the 30's% for the other boss fights
What I was expecting, over the course of 3 hours, is to be close to 40%.
Individually, the fights could range from 30% to 50%, but actually they linger in the 30%'s
hence, my suspicion that the Mbarr proc rate was nerfed
Done some tests and the proc rate seems okay:
Casted Arcane Blast four times, wrote 1 if there was a proc, wrote 0, if there was no proc.
Grouped it in a 10x10 table:
I II III IV V VI VII VIIIIX X
I0011111111
II1111111111
III1101111111
IV1101111111
V1110011110
VI1100011111
VII1011111011
VIII1111101111
IX1100001111
X1111101111