Even though Moroni saw similarities between the Nephite battle at Cumorah and the Jaredite end at Ramah, there were differences. Mormon describes only a single, terrible battle. The Jaredite battle raged back and forth.
Coriantumr again attempts to end the conflict, but things are too far gone. They were on their way to destruction.
Another important difference between the end of the Jaredites and the end of the Nephites is that there was a victorious army which defeated the Nephites. There were clearly losses on both sides, but only the Nephites were destroyed.
In the case of the Jaredites at Ramah, both contending armies are Jaredite. Thus, for them it was a mutual destruction. There was no victor. Everyone lost.