I know that kyurem has the power of zekrom and reshiram
but what about dialga,palkia giratina and arceus?
Dialga controls time and its a dragon/steel type, Palkia
controls space. Giratina can enter the reverse world and arceus
is the God of all Pokemon.
Kyurem isn't the strongest Dragon-type. Its total stats are 660, whereas it is 680 for Dialga, Palkia, and Giratina, and 720 for Arceus. If you want to experiment, get the event Palkia and try it, battling it against a friends Kyurem. chances are palkia will win.
Hope I helped