Mega-Octane is not a good name. It's not easy to say, nor is it memorable. Scourge however is all these, plus it's really villainous sounding.
It's plausible early early on, they thought about naming him Octane. It's obvious now that was no longer available, hence the modifier Mega-Octane. Not that normal Octane was a great or intimidating name for the new series villain. But with the new modifier, it was clunky, and even worse. So if he ever was going to be Octane, the change was no accident, nor was it a mistake.
If it was another year or two later, he'd have been named Nemesis Prime.
Dark Convoy only works in Japan where your Autobot leader is called Convoy. I can see some good reasons why they might have avoided the name Dark/Black convoy in the US and they were a year away from the first Nemesis Prime.