The weight limit counts stuff that goes into the UTXO set more than it counts the rest. It doesn't have anything to do with aggregations or discounts or whatever--  it's just the limit on what can be in a block recognizes that UTXO data takes more resources.  Neither signature data nor op-return stuff goes in the utxo.   In all fairness the up-weighing ought to be much higher but there is a tradeoff vs how much bandwidth people can cause if they make unusual transactions with more witness data than typical... and a subset of users are more bandwidth limited than memory/io/etc. limited.