There is a reason why Jean nodded at this proposal
Before, he came here he reads the result of the debate in the Senate about this matter.
The seas that they chose to protect their new continent changes many times during the debate. Some said that the Sea of Light is better. Other suggested the Cloud Sea. But most of them wanted the Whirling Sea.
Since Pandemonium probably would choose the Turbulent Sea, then they should choose the Whirling Sea
The Whirling Sea is a sea that also have characteristic of the Turbulent Sea and the Illusory Sea.
The only downside of the Whiling Sea is that it is more unstable than the Turbulent Sea.
This is not to say that the Turbulent Sea itself is stable. But when compared, it is clear that Turbulent Sea, for all of its horror stories is not as terrifying as the Whirling Sea.
Not to mention, that Jean wanted to use the characteristic of the Whirling Sea to increase his understanding of his own Time Law.
