The problem is simply the fact that the powersets come from players and are not really designed to work for mobs as well, due to the stacking issue. All of the powersets and especially their secndary effects work well when alone, or maybe two of them.
But then the standard spawn is not one or two mobs, it's about 10 of them in a team. So that means the little debuff can become huge, the little damage can become huge as well, and the bigger ones... well they become completely overpowered.
So when making a story arc i'm usually locked out of 90% of the powers available to mobs. Let's take offensive powers i want to give to a minion or LT:
-dark blast/melee ? No thanks, i don't want to stack tons of -tohit on the players, it could work for high levels but it would make the arc not fun at all for a lowbie
-energy ? Energy blast is okay, KB is not that bad. Melee ? No way, let's not even take into account the high damage, but stuns everywhere ? Those minions could probably stack enough stuns to stun about anything if they all had EM.
-Rage for higher settings, no way. Not sure how it is on test, but right now they come with a full attack chain on STANDARD (i think 4 powers). Minions like that can destroy any squishy in no time, not really good.
-Rad blast and the crazy def debuff ? Huh, no thanks.
And the list could go like that forever because almost every set has a secondary effect, which is perfect as minor bonus for a player, but turns into hell when you're facing 10+ mobs with those powers. The only set worth using for me right now are weapon sets (the def debuff is not that bad) and martial art sometimes, although i get a lot of complaints from ATs with no mezz protection when they're perma-stunned and defeated by minions unless they bring tons of breakfrees.
Considering the custom mobs are already on the high damage side with their modifiers for powers, i think removing or greatly reducing the secondary effects according to the difficulty settings would help a lot. There's just no way i'll ever use the dark, rad or even elec sets when i know they have the potential to completely destroy a player hit chance, defense or endurance before they even get the chance to do much, and i'd appreciate if i could create mobs with something else than dual blades or claws.
