I always think of summoning primals as a game of "Wish Corruption" sure you get something of what you want, but there is a twist or a price you didn't expect.

That's why Bahamut wasn't the Bahamut that Tiamat wanted for example, but also depending on one's emotional state since even the Ancients aren't perfect with creation magic.

Even at our current state, we who may have been one to summon Hydaelyn is now summoning Leviathan with 2 heads and Titan as the wheeled warrior.