To be fair i can understand why they include this many Dio's, i mean he is a pretty important character, and all of his different versions most likely have some very different movesets.

Well, DIO has been a driving force of EVERY SINGLE JOJO PART.

It has always been about fighting him, finding out about the source of his power, or dealing with his minions.

So if you have to have someone fuck with time and alt realities, might as well make it Dio. Hell, that is EXACTLY WHAT HAPPENED IN PART 7- they had alt realities, and said -"Fuck it, make Dio the final boss again".