Not true, at least not if we buy into the continium of conflict found in Clausewitz (I happen to). Very brutal COIN efforts may appear to eliminate an insurgency, but the effect is only temporary. A generation or so later, the insurgency re-appears and is ever more brutal and violent.
Saddam's attacks on the Southern Shia did restor order for a time, but, as US forces enetering in Najaf and Karbala discovered, there were certainly Shia resistance forces in the area.
How mant times did Britain try and solve its Irish problem through brutality? And in the end the Isle was divided and the last counter-insurgency seems to have effectively put the issue to rest on a large scale (still some minor criminal groups hiding behind the IRA mantel).
we can also look at German actions during WWII in the Balkans and other areas, and these areas were hardly pacified even in the face of near total German brutality.
The Balkans themselves are a case study in how brutality can tear an area assunder. the tangled hostory of one groups hero being every other groups villian points to the problems of brutality as policy.
Brutality, particularly in the modern world, can have dramatic effects. The Kosovo ethnic cleansing provoked a massive NATO military intervention.
Brutality in Burma may have capped the immediate problem, but would you be willing to bet that it is the last unrest generated by the inequalities and injstices in that system?
In the end, brutality rarely works as a comprehensive solution.