Shiva wouldn't be the real thing either.... she's dead. No primal is the real primal - they're all figments of the worshippers imagination fuelled by their own desires and wishes.
Ysayle thought she summoned shiva, but only summoned a shade reflecting her own desires.
Look at what Tiamat said - when Bahamut was summoned he was summoned as a shade of his former self. The only person capable of summoning anything close to Shiva would be Hrasvalgar (sp?)
