I think the thing is, the Franco-Prussian war was a limited war with limited goals. The reason why the Napoleonic war stands out as the last war of significance is it was an unlimited war, which reformed europe after it.

I don't think casualty counts are particularly good metrics here - rather, the metric should be the degree to which the civilian population is brought into the war, as victims, soldiers, or workers. In that sense, the colonies had been experiencing 'total' wars in the sense that, europeans rarely distinguished between civilian and enemy forces when putting down insurrection, and rarely had qualms about mass conscription in various forms. Consequently, the casualty numbers and social destruction of the first world war, while extremely unusual for europe, would have been far less unusual in east Africa, or India.