Two observations:
1. His point that state lost control over its citizens and is obsolete is simply not true. The state might have lost some control over some aspects of everyday life, such as production and dissemination of information or purchasing of certain commodities, but it gained control over other aspects. And more importantly, the effects of that shift of state control was very uneven on different social classes. The working class is subjected to more control, the capitalist class - to less. It seems surprising that a Marxist historian missed that dimension.
2. I think that the perceived barbarity of the 20 and 21 centuries are a function of salience and expectations. Unspeakable barbarities were committed before that time, yet they remained largely unseen because the means of recording and disseminating images of these barbarities did not exist. Secondly, the post - WWII growth in standards of living, social welfare protection, progress in science an international cooperation created high expectations about a life free of death suffering and disease. By these high standards, today's warfare, or for that matter, poverty appear unacceptable - even though they are quite minor by the pre 20-centure standards.
Wojtek