However, Sacred Fire is your only way of hitting Dialga and Jirachi for good damage. Even in rain, Support Dialga hates taking burn damage all the time. Jirachi does not enjoy burn either even in the rain. Skarmory hates Sacred Fire and can only wall you in the rain. This Ho-Oh set has so much Special Defense it will attract physical attackers such as Zekrom so Sacred Fire can deter them from switching it. Also, Ferrothorn can Leech Seed and out stall you if you drop Sacred Fire which is just bad.
Sacred Fire hits the Poison/Steel types who are immune to Toxic though. Brave Bird can still be the main option however. I am thinking about like this:
Brave Bird
Sacred Fire
Roost
Whirlwind / Toxic / Light Screen
You don't need Toxic for Latias anyway because you 2HKO with Brave Bird. Yeah Brave Bird main option for more PP, consistency and accuracy.