It’s worse, jno, because of the nature of the entire event in which he became involved.
Had he been alone on the roof having just gone there for his own purposes the charge of violent disorder would not have been brought. It is the enterprise in which he was involved which is the aggravating feature. The effect on the public (and the police) of a baying mob is far more severe than that of an individual and it is that which has been recognised in the charge and the sentence. With no apologies I quote again from the Court of Appeal :
“A feature of the offence is that it is not the individual conduct of one offender that is of importance but the nature of the offending as a whole.”
This is in my view the most important aspect that led to this particular sentence. He was part of a mob that clearly set out to terrorise the area and cause as much damage and mayhem as they saw fit. The fact that he seems to have been the only one apprehended and charged (at least with violent disorder) is not really relevant. He took probably the most prominent role in the enterprise which must have been extremely disturbing for all concerned, especially the policxe officers charged with the task of sorting it out.
He chose to do it, he is old enough to know better and, as has been said, the sentence might just deter some others from behaving similarly with possibly more tragic consequences.