You are thinking of “social mobility”, which is a term of art that doesn’t mean what people assume it means. It is essentially a zero-sum rank of your income compare to your neighbor. You can become poorer and still be “socially mobile” or much richer and not be “socially mobile”.

Social mobility has very little to do with increasing your economic welfare in any absolute sense. It strongly favors countries with highly compressed wages and doesn’t imply much about ease of increasing income since it is only weakly correlated with that.