Translation

幻想にすぎない / 実体のない / 錯覚による

Meaning

Illusory means seeming real or valuable but actually not real, not reliable, or not effective. The trap is using imaginary for every case; illusory often criticizes a belief, promise, benefit, or sense of control.

Examples

• その割引による利益は、手数料を考えると幻想にすぎませんでした。
  The benefit of the discount was illusory once fees were considered.
• 契約書の保証は実体のない約束だと判断されました。
  The guarantee in the contract was found to be illusory.