I’ve always had the impression that cable pull and RD actuation movement, especially of older systems was not consistent from shift to shift/cog to cog.
As far as your older 90’s Campy setup, I thought the RD actuation ratio was 1.4:1.
I believe the new Shimano Tiagra, 105, GRX actuation ratio is 1.4:1.
It might be possible to run 9 speed Ergos to a Tiagra/GRX RD instead of a Campy RD.
John