The best metric we used when optimizing low latency systems was fixing the slowest outlier. Maybe a similar metric could be used for economies eg focusing on the worse off person.
I recommend you read John Rawls's seminal work A Theory of Justice.
For him, there are three principles a society should be based on (in lexical order):
Maximum, equal liberties for all > Equality of opportunity > Difference principle
Difference principle: Any inequality has to be to the biggest advantage for the least well-off person