A wireless access node simultaneously serves wireless User Equipment (UE) over Fifth Generation New Radio (5GNR) and Long Term Evolution (LTE). A baseband unit splits user data into a 5GNR portion and an LTE portion per a dynamic 5GNR/LTE split. A 5GNR radio wirelessly transfers the 5GNR portion to the wireless UE. An LTE radio wirelessly transfers the LTE portion to the wireless UE. The baseband unit corrects LTE and 5GNR transmission errors and determines a 5GNR Block Error Rate (BLER) and an LTE BLER. The baseband unit modifies the dynamic 5GNR/LTE split based on the difference between the 5GNR BLER and the LTE BLER. The baseband unit splits additional user data into 5GNR and LTE portions per the modified 5GNR/LTE split.