That may be a factor, but the UK has other Caribbean carnivals that do not seem to have the same level of crime and disorder as Notting Hill.
Jamaica is an interesting comparison. Around independence it had a very low murder rate, but over the following decades became one of the world’s higher-homicide countries and also fell well behind economically. Singapore, by contrast, became independent with very few natural resources and serious social and economic problems, yet developed into one of the safest and most prosperous countries in the world.
It is obviously not a like-for-like comparison, but it does suggest that the culture and people driving institutions, governance and policy matter at least as much as natural resources or the legacy of colonialism.