Deviating from his original plan might not be a great deal to the immortals, but it was to Patroclus. At the chief architect of the future society, he knew if he didn't lay the foundation straight, the world he built would collapse as it grew.
The immortals were aware of Patroclus's ultimate goal, but doubtful that it was realistic.
Outright destruction would be much easier than slow integration and assimilation. When the Immortals had quashed all resistance force, it would be much easier to convert the human population; even then, it would take up to decades to complete the task.
And now, Wang Tong's appearance had given the human population hope and rekindled their desire to fight back.