To add on to what was mentioned about "Rebirth" being only 3 episodes - it would make sense to extend the series to 5, since certain other transformers were not introduced:
Powermasters (transformers who's Nebulan counterparts transformed into their engines, without whom they couldn't transform - Optimus Prime would change into a Powermaster, who could also transform into a giant robot);
Autobot Quickswitch (Sixshot's "son", who could also change into 6 different forms);
The Targetmaster Seacons (6 Decepticon sea creatures that combined into Piranacon; the 6th member became Piranacon's weapon and was thus interchangeable, except for Snaptrap, the main body);
Sparkabots and Firecons (transformers that had sparks fly out of them); and
Monsterbots (3 Autobots that transformed into monsters).