As I pointed out in the other thread Vesper, mining yield cap is 3, same as fishing. The only significant desparity is logging at a cap of 5.

Actually mining hardcap for high rank items is actually 1. Gems, all Gold, and Mythril is capped at 1.
For refference top wood, Mahogany, is also capped at one log.

If anything should be adjusted, it should be logging down to a cap of 3 for MH, not an increase to fishing.
When high ranking fish can still be caught at 3 per, while other skills are capped at 1, I'm not sure really what you are complaining about.

Please give examples of specific materials that you feel are imballanced.