I have an answer, They dont want to waist so much time by using episode after episode about how there Bakugan evolved, like they did origanally. So mayby We might see them in a few flash backs, or other people using them, look at how this looks below.Dragonoid > Delta DragonoidSkyress > Storm SkyressThunder Wilda > WildaMega Nemus > NemusLook at the underlined parts, when the Bakugan evolved in the original series they added another part to their name, While if what you all say, then the new series will break this 'series'. Also it makes more sense for the better version to be the evolved version instead of the worser version.
Yeeaah... worser isn't a word. XD Though we know what you mean, it doesn't sound right. The word you're looking for is pre-evolved, previous, or worse.