You really need to go back and read. I've addressed it multiple times.
The rotation can handle one pitcher in this situation not 2. Trying to cover the innings of 2 pitchers who will likely miss innings is to difficult. They needed to get rid of one of them. Since Rodon did not have a contract and Kopech is cost controlled, he is the more logical one to keep.
Yes, someone like Lopez or a bullpen day will be needed to cover maybe 6-7 starts for either situation bit the rotation can't handle 2 pitchers in that situation.