When Chen Yu initially constructed his Necromantic Space, he stole half a tributary of the Nether River from the peninsula opposite Japan. Although he merely punctured a small hole in one of the tributaries, even so, it drew away a tenth of the water flow from the Nether River passing through that peninsula.
At first glance, it might seem like Chen Yu stole a significant amount, but in reality, it was because the water flow of the Nether River passing through that peninsula was so minuscule that even such a small diversion claimed a tenth of its volume.
Compared to the methods used by other pantheons that essentially create new tributaries directly from the world's main Nether River, the tributary passing through the peninsula seems more like an offshoot of an even smaller sub-tributary.
If Chen Yu hadn't been so weak back then—barely having just transitioned into a Necromancer—he might have been capable of directing half that tributary over to his space.
