The Tower of Heaven could control the world's internal climate, earth, sea, and everything within the World of Titan. It was the control hub of the World of Titan but limited to controlling of the insides of the World of Titan.
The Tower of Heaven didn't have the ability to control the movement of the World of Titan, much less attack or defend beyond the World of Titan, hence it wasn't as powerful as what Mientte and Wendy had previously thought.
But Wendy was clear-headed. She knew that Lu Zhiyu would never leave behind the authority to control the entire World of Titan in the Tower of Heaven or even the ability to interfere with the outside. If that really happened, if the tower spirit really became the owner of the World of Titan, with the massive power of the mythical alchemy tower and the power of a whole half-bitwall, no one in the entire Starsoul World could be on par with it.