The problem I have with Convobat being Prime is that the "Maximal Upgrade" had nothing to do with the adoption of a 'Beast' mode - it was the adoption of a smaller, efficient, Proto-Matter body.

Transformers were still machines and robots. BW:Gathering and Ascending depicts Cybertron covered with robots - cars and motorbikes and such, not animals with fur and hair and scales.

So Convobat coming out of the upgrade as a fleshy Bat is debatable.