So in the original game when the wither storm fakes its death after it wakes up the middle wither storm looks like phase 5 and not big brain

Making models are hard. He'd have to make an entirely new Wither Storm model so it has the separation blocks (of where the 2 other Wither's were supposed to be), plus, I feel it wouldn't look right.

Yeah, lot's of model reworking which isn't worth it. Besides, my models are basically the "image" of my mod at this point so changing them doesn't make much sense.

Also, In MCSM the size doesn't make much scence, given how massize phase 5.5 is.