High copper might be bad, but no copper is just as bad for the plants.
Like most chemicals, too much, kills the patient, not enough does not cure the disease.
You need some copper.
Just not a lot.
Some vendors go too far and assume it's all bad, like NO3 and PO4 with plants, many assume that it's bad, yet the plant obviously needs a lot of these to grow.
Most folks today realize that NO3/PO4 are not bad, as long as they do not get extreme, like the copper, in the proper range that allows for good plant growth.
Regards,
Tom Barr