RDM melee damage was terrible, and their magic damage was even worse, even with Double Cast. Their melee damage outscales their magic damage because RDM are barred from obtaining the best magic, but not barred from wearing the best equipment. In FFV, I distinctly remember Dancers dealing more damage in general than RDM. Even the FFV BRD had its damage role niche by demolishing undead and dragons.

To be able to compete at all, non-MMO RDM were relegated to a role that utilized spells that didn't scale with stats. In other words, buffing and debuffs. Doublecast allowed them to throw out more buffs and debuffs sooner.

Some people hated how the FFXI RDM played in groups because they wanted them to be melee DPS to match their french musketeer look. Other people, like myself, hated how the FFXI RDM turned out because their only support ability of any value was Refresh, turning them into nothing more than Refresh bots.