That's fair. I think there is good value in building up a historiography of political thought. In fact, that is the only reason why we still talk about Marx, Engels, Lenin, Mao, etc. After all, there are much more modern writers who can speak much more accurately about the events taking place in the world around us, but it is the ability to trace modern problems to their original roots which really helps us sort out reality from pop philosophy woo. Considering the progression of philosophers included on the chart, Locke does probably belong there. Adam Smith even more so. It certainly helps to be familiar with an ideological framework if you are trying to refute it.