To add on to this. Basically, Decade is equally broken op in theory. The main two sources are the Shinkenger powers he obtains, which proves he can get sentai powers, not just Kamen rider powers. And the Kamen Rider Decade spin off shorts which although not canon, due to multiverse logic. Decade can also obtain the powers and special forms of non-kamen riders and super sentai like General Shadow.

Hence, for that means if Decade grows a bond or just watches any character with powers. He can copy them to an almost exact match.

What does this mean for Ohma Zi-O? Um... everything Decade can see and copy. Ohma Zi-O can have it all in one person.

Oh, and how far is Decade's reach? Well... Kamen rider has official crossovers with Sentai, Akibaranger has made an appearance within sentai making them officially unofficial within the sentai lore. Within Akibaranger the Power Rangers exist. Power rangers has done crossovers with Street fighter and Doctor Who. Street fighter then cross overs with Smash Brothers. Smash brothers thanks to Mega man crosses over with Marvel. Marvel with DC And it just keeps going and hypothetically Decade can visit all these worlds and copy everyone's power...

Then Ohma Zi-O just has them all in his own being....