I would suggest to switch Aggron. He feel a bit out of place, mainly because of its typing. Steel/Rock have many very bad double weaknesses (mainelly ground) that is awefull for the game. Even whit a Rock Head + Head Smash set, he is still weaker that Regigigigigigigigigigigas in terms of overall damage output. Also, Regigigas brings more speed to your team, which is always welcome.
It would look like this:
D. Gallade
Mega Eevee
Primal Regigigas
Delta Bisharp
Primal Giratina
Zygarde