Simply declaring that all exalts have access to sorcery of a higher tier would break the setting. If DBs had access to celestial circle, and Lunars/Sids could use solar all along, history of the setting would be vastly different.

BUT, if you made this improved access a new thing, it could work. Blame it all on the Great Contagion and Balorian Crusade. The vast alien energies that flooded Creation had a greater effect on the essence of the world than anyone could have imagined. Add in the heavy use of the Sword of Creation/Realm Defense Grid. It was never tested for such a heavy...