Low Ice Maker Water Line Pressure
When you talk of bad flow at the refrigerator ice maker I am assuming you are looking after the fill valve of the fridge .. because an open ended copper pipe should flow plenty of water - if the pipe has no restriction (clog or kinked).

If that is fine and you are checking at the fridge valve:


Fridge Valve is defective partially sticking.
Fridge Filter Cartridge is bad or defective.