"This is because auto-attacks are based on strength, which RDM has next to none of. Therefore, it can be concluded that all oGCDs are magic damage."

RDM's INT stat controls its physical damage as well as its healing potency. To claim otherwise you'd be claiming Holy Spirit was physical damage just because PLD's STR stat controls its damage. When a tooltip says "Delivers an attack" like Fleche and Riposte do, it's a physical attack. Enchanted Riposte reads "Deals unaspected magic damage" as a comparison, meaning the damage is magical.