>Well, isn't this exactly what people try to do when comparing these systems? Number of deaths, number of people in poverty, number of products on the shelves in stores?
Not necessarily. Qualitative models have been increasingly adopted, and most arguments from the socialist side of the debate concede that capitalism has greatly improved quantitatively measured standards of living, it is responsible for a huge range of products, and that 20th c. socialism lead to many deaths. Qualitative criticisms are the most popular today in political economy, namely, the work of Sen, Roemer, Vrousalis and others on qualitative (with some quantitative basis) concepts of "exploitation", "domination", "alienation", and "fetishism". Nevertheless, quantitative arguments are also abound, in particular debate over what classifies as "poverty", and the transformation of values to prices of production (usually formulated mathematically). The road to defining axiomitically concepts like "exploitation" still has "a million miles to go" (Veneziani and Yoshihara).
This area of criticism, in my opinion (and the opinion of Honkanen[0]), needs more quantitative reasoning, and qualitative thinking cannot simply brush aside the use of statistics, which is relevant in many (but not all) instances.
[0] Honkanen P. (2020) The Transformation Problem and Value-Form: Methodological Comments. In: Silver M. (eds) Confronting Capitalism in the 21st Century. Palgrave Macmillan, Cham