No skaven player should be allowed to complain about brokeness. Even more when complaining about things that haven't been tested yet, and that HAVE weakness. I'm not talking about manouvers or steadfast. I'm talking about models expensive points-wise, with Initiative 2 and Leadership 7, surrounded with low model count units.
Low initiative is a GREAT weakness. Not only in Combat, but against the well known Ini-test spells (wich skaven have 1 that remove models, if i'm not wrong). Sum the big bases to that, and you have a unit that can be killed with a non powered pit of shades or a pendulum (or the skaven ini-test spell).
Leadership 7 is another great weakness. They can be panicked with ease. Just kill the easier to kill units near, and make them pass the test or run.
Yes, you can use General's leadership and BSB re-roll, but Ogres would have a hard time protecting their characters from cannons, stone-throwers and so on, because the low model count of the units, so easier to remove the LoS save (remember that the unit's champion doesn't count for LoS purposes, so to protect a character one Ogre player should protect his characters with at least a 6 model unit, counting full command).
So..... Good? Yes. Broken. Absolutely not.
Tools to deal with them in no-close combat.
Death magic: Purple sun. The signature spell too.
Metal magic: Obvious. Signature spell.
Shadows: Pendulum, Pit of shades.
Skaven magic: The ini-test spell.
Cannons, stone-throwers, Bolt-throwers. Multi-wound warmachines.
Handguns. Massive shooting. High strenght shooting (Jezzails).
These things don't require a special tactical genius to use. The mournfangs are not like an HPA or a hydra (who have high chances of killing an entire 3 model unit in a single round, obviously taking some wounds in return...).