Far more powerful, on all aspects, not just destructive power. I don't know all the rules of the Nasuverse and I don't want to say silly things, but let's just took one example :
Caligula is blessed by the Moon goddess Diana and can use the moon's shine to make everyone insane. Ishtar is a Venus goddess and can just use the planet's heat without restriction.
Oh, that was your point all along... Then yes, more powerful than the beloved, invincible, perfect, golden, super arrogant Babylonian King of unlimited wealth, Gilgamesh McSpamTreasuryToWin.
That's the whole point of the Noble Phantasm, so yes. Most likely.
Not Going to work on Parvati,Shiva or Any extremely powerful Gods. Chains of Heaven has limits.
I apologize if I am simply unaware of something, but why wouldn't it work on Parvati or other powerful gods. I don't remember something like this being stated, although it could be real. But is Parvati really that strong? Again, I might be simply misinformed. but she doesn't seem supremely powerful when summoned as a Servant at least.