It always look to me that pushing Cyborg is a decision from the WB higher-ups. They need diversity in DCEU, they saw Ironman being popular and sold a lot of merchandises, they probably knew Cyborg from Super Friends or Teen Titans cartoon.
Vic is not even among the more popular charcters in NTT, Donna Troy probably has more fans than him, he's also probably the least popular member in Teen Titans cartoon, less than Terra, a character only appeared in handful of episodes. It would be weird if an industry veteran like Geoff Johns thought it is a good decision to push Cyborg as the top black Superhero. He didn't show much interest in the character during his Justice League run either.