The proportion dosen't seem as morally relevant (though it is a factor) as the sheer number (you can figure it as a trolley problem; the train running over 10k out of 100k is arguably worse than running over 5 out of 10) - and arguably, inequality, exploitation and domination have more to do with relative wealth than absolute wealth. Although the lives of a great many have undeniably improved, that has nothing to do with what social scientists and philosophers of economics mean by inequality, exploitation and domination - which usually focuses on the share of productive capacity by members of society. All the "big names" like Sen and Roemer have those issues on the radar. You can figure the problems of the system in terms of domination[0], exploiters dominating[1], extraction of surplus-value[2], or unequal exchange of labour[3][4].
If it's the sheer number you care about, not the proportion, then the problem is clear: Human reproduction. Eliminate that, and the sheer number of incidents of oppression and suffering will go down.