What the Report of the Commission of Inquiry on Syria reminds us is of the inadequacy of genocide law as according to the legal definition, the ‘crime of crimes’ can only be perpetrated against ‘racial, ethnical, religious and national groups’. The fact that other collectivities cannot be victims of genocide, especially when the intent to destroy that collectivity is clearly present, is a serious limitation of the defintion of genocide both in the Convention on Prevention and Punishment of the Crime of Genocide as well as the Rome statute. If genocide is to retain its status as the ‘crime of crimes’ its essential that it also protect other collectivities who have been historically targetted for destruction as well as collectivities who may be so targetted in the future.
However even assuming that genocide law in a future incarnation covers an open list of groups who may be targetted for extermination, the question as to why should a crime committed against a collectivity necessarily be seen as more serious than crimes committed against numerous individuals who are not a collectivity, remains. 
If one refers back to the situation in Syria, clearly the crimes committed by the regime including disappearances, sieges, attacks on medical facilities and indiscriminate aerial bombardment dwarf in sheer quantitative impact the crimes of ISIS. However these crimes would fall within the legal definition of a ‘crime against humanity’ and ‘war crimes’ and would not come within the legal definition of genocide. If we consider that the regime is responsible for the vast majority of deaths and displacement in Syria, the moral cul de sac into which a focus on genocide as the ‘crime of crimes’ can lead us becomes apparent.
Philippe Sands in a marvelous book part legal history part personal history incisively traces the history of the two terms genocide with its focus on the group and crime against humanity with its focus on the individual to two eminent legal scholars- Raphael Lemkin and Hersch Lauterpacht respectively. Both men had a personal stake in the development of these terms as they both lost their close family in the holocaust. The difference between the two viewpoints was that for Lauterpacht, the individual was the focal point and the reason for the atrocity was not an ingredient of the offence. What was important was the atrocity was perpetrated on a ‘civilian population’ and that it was ‘widespread and systematic’. However for Lemkin, the focus was on the reason, i.e. the intentional destruction of the collectivity.
While ‘genocide’ is a powerful way of capturing a crime like no other, namely the intentional destruction of an entire human group there are clearly limitations to the concept. Firstly the groups who are protected are too narrowly defined and secondly atrocities regardless of scale if they are committed without genocidal intent will always be seen as a lesser crime to genocide. This has ethical moral and socio-legal implications.
Thus while genocide may be the appropriate way of analyzing the harm visited on the Yazidi community, the term itself as currently defined lacks the suppleness to respond to different realities. As the Syrian civil war teaches us there is a gap between the ‘material seriousness’ of the crimes committed by the regime and the ‘juridical seriousness’ with which those crimes are likely to be treated as long as genocide continues to be seen as the ‘crime of crimes’. 
 See Payan Akhawan, Reducing genocide to law, Cambridge University Press, Cambridge, 2014.