I have disabled other hostile mobs spawning, except for Troll and warrior skeleton in 1.2.3a, and I have found out that even with the lowest spawn weight, they still constantly harass me, as soon as I switch to hard mode, they spawn everywhere

Yeh this is my mistake. I need to add a dummy entry to counterweigh the weights. I will push this in the next update!

Added the filler entry in the newest Multimob. Im not sure if its 100% fixed but let me know if this improves it.