Already have Hyperion at rank 5
Corvus is pretty much unusable in 6.3 and beyond if you're not running suicides. Medusa hasn't aged well and Cull is better with the reduction in attack values but still not great.
The only reason I am hesitant about Corvus is that I am not 100% sure how useful he will be in content I am focusing on (variants, cavalier main/side event quest, and 6.3).Also, I can r5 Venom as well