What armor a class wears is pointless if the only thing that matters is base stats on each piece. With glamour it's actually even more skewed since you just take gear with the best stats and glamour something you like on it.

Technically one of the Red Mages de facto skills to offset it's lower spell pool was Dualcast(let's be honest swiftcast kinda already does this unless they make RDM do it all the time) or the ability to chainspell. If the BLM doesn't get Annihilation in next expansion Red Mage might get it since it combines Fire and Ice together. Albeit at a long cast time/cooldown. Maybe 5 minutes cooldown and a 10 second cast time.

What is Annihilation? Ascian Prime spell. Running by the game's jaded lore concepts it looks like probably the ultimate BLM spell.