I’ve never used copper on tomatoes. I have used neem. Usually I just pick off the bad leaves or pull up the whole plant so it won’t affect its neighbors.
Copper deficiency can increase sterility in offspring of vascular plants. A surplus of copper can be detrimental to most life forms. Dosage is key.
I would assume it mainly directly kills bacteria and fungi because high concentrations of copper tend to kill things. And that you’d want to apply it in a form that isn’t absorbed by the plant (copper hydroxide for instance due to its poor solubility) and just gradually leaches copper ions to kill microbes