...that would make more sense, but alas no. Optimus Primal was definitely still called that on Cybertron as those who knew him on Cybertron (and other off-world Maximal colonies) knew him by that name when they later encountered him on prehistoric Earth (e.g.: Depthcharge, Ravage) and when he temporarily was transported to the planet Gaea (e.g.: Lio Convoy etc.).

There are exceptions to this... Airazor and Tigatron only adopted their names after coming to Earth and scanning alt modes - on Cybertron they had other names which they'd since forgotten after nearly being killed fighting Buzzsaw and Laserbeak. BW Megatron was originally known by a different name until the theft of the Golden Disk, after which he intentionally renamed himself after the reknowned Decepticon leader (as Ravage once said to him, "You have his name, but not his army.").

A lot of other BW TFs who were 'born' on Earth obviously only adapted names there. Protoform X never officially had a name other than that until he joined the Beast Wars and was assigned the name "Rampage" by Megatron.