As has been said in this thread, in order to compete, you must field a force that can survive Wrathful Skies. This forces everyone to use the same small subset of units (lightning immune leaders and units). The great variety of unit types present in the game (and therefore, in my opinion, a lot of the flavor) is rendered meaningless.
Even if Wrathful Skies was more difficult to cast, the ability to build gem producing items combined with the superiority of certain summoned units, makes national units unviable. Similary, unit producing items (i.e. soul contracts) product the same effect. Why have any unit except a devil (assuming you have any units at all, you could just field leaders) ?
The game is deep and it is a shame that MP is reduced to a few units and strategies. I'm not very experienced, but from what I have seen and what I have read this is true.
But, I've heard a lot of good possible solutions that would make more units viable. I would love to see large armies of both National and Summoned troops backed up by mages and not just mage armies and SCs.
Regardless, I'm having a blast
It's good to see Illwinter here discussing this stuff. It bodes well for Dom 3.