Additional crit damage could be a flat addition instead of a multiplier

[red tinsel]

Some examples:

Character has 0% base crit damage bonus, and gets +20% crit damage

Multiplier (current): they still have 0% crit damage bonus.
Additional: they have 20% crit damage bonus.

Character has 200% base crit damage bonus, and gets +20% crit damage

Multiplier (current): they have 220% crit damage bonus.
Additional: they have 240% crit damage bonus.

Decoupling bonus crit damage from the baseline crit multiplier makes the stat's effectiveness much more consistent and intuitive across characters (+20% means you get an additional 20% of pre-crit damage, no matter what you're playing); this also allows tinkering with the baseline critical multiplier given to each character without throwing their crit effectiveness wildly out of balance.

This also means you can have characters without inherent crit, while leaving it open as a lategame scalar once people have run out of other things to invest in.