Yes, there are NO bugs in this game - they are ALL intended features, part of Nival's master plan
As it stand IM is something you can easily do without, actually Warlock will do better if IM is taken out completely, isn't it? Just rename it to Elemental Damage proficiency racial, leave the ED bonus and that's it.
One thing that stroke me in all those pages is how when somebody suggested a change to IM the first two reactions were that BDs would become overpowered or Armageddon will become overpowered, no one seem to miss the ability to penetrate the enemy units immunity (there are very few non-Dungeon units in total that are such and all of them are a lot "less" immune compared to BDs). In all comments IM is seen more like a brake, a limiting factor put there to ensure that Warlock's empowered spells don't get out of hand.
It might actually be interesting to see what the results of small poll that asks Dungeon players whether they prefer to have IM as it is or lose completely the ability to pierce enemy immunity but also not being able to harm their own Black Dragons, i.e. you eliminate IM completely, leaving only the ED bonus. What do you think people would say? Because for me IM is not even necessary - BDs are the single most affected unit by IM and its affected in a purely negative sense, even though a racial is supposed to give a distinct advantage, not disadvantages. How many factions except Dungeon have immune creatures or highly resistant creatures as to justify IM? Hmmm?
Additionally IM seems to be in a minority of game features that is just as harmful as it is advantegeous. For example - the Hydra's six headed attack - how come if you have friendly and enemy units next to it it selectively harms only the enemy ones? Why not apply the IM logic here and make it harm all with the same line of arguments that it will require more brainpower and you should be carefull with what you place next to them? Or Cerberi for that matter? Because IM is just like that at the moment.
Another example - how come you have a choice of whether to cast empowered spells or not? If they worked the way IM does you shouldn't have had a choice - it should have been enforced on you too and so from the very beginning - sure you get the advantage of casting more powerful spells, it just so happens that it costs you double, i.e. how come I cannot chose whether to cast Irresistible magic spells or nor - how come it is ALWAYS irresistible? How come Warlocks cannot cast a "simpler" type of spell if they wanted to - everybody else seems to be able, no?
IM is an enforced "bonus" that just so happens to hurt BDs the most, your own tier 7 upgraded units - someone explain to me why is IM supposed to be such a big advantege for me exactly? Other than the secondary racials is there any other substantial reason you would want to get it? Because when you do you will play your BDs the way you would if they didn't have any immunity, isn't it? So what advantage is it TO YOU that YOUR BDs have immunity exactly? Hmm? And people think IM is ok? Really?
. You can also lower Armeggedon damage, use AA to help stop some of that damage, or even create a spell that would protect units from Armeggedon. Something like Divine Protection, or Dark Protection, or Protection of Earth (light, dark, summons respectfully). So that way there is a nice counter for the spell. Bring back Dragonslayer too 
