It proved to be a Pyrrhic victory.

Meaning

A victory that comes at such a great cost that it's essentially a defeat.

Examples

• John: So, you won the contract?
• Alice: Yes, but it proved to be <b>a Pyrrhic victory</b>. The costs were far too high.
• John: Oh dear. That's disappointing.
• Alice: Exactly. In the end, it was <b>a Pyrrhic victory</b>.