A Pyrrhic defeat?

If the victory was so costly it led to defeat, then its opposite would be a loss that was so advantageous it led to victory:

Gambit

2(In chess) an opening move in which a player makes a sacrifice, typically of a pawn, for the sake of a compensating advantage:

Pyrrhic Defeat Theory suggest increasing power by increasing the cost of a battle:

the idea that those with the power to change a system, benefit from the way it currently works.

Origin

In criminology, pyrrhic defeat theory is a way of looking at criminal justice policy. It suggests that the criminal justice system’s intentions are the very opposite of common expectations; it functions the way it does in order to create a specific image of crime: one in which it is actually a threat from the poor. However, to justify the truth of the idea there must be some substance to back it up. The system needs to fight crime, to some extent at least, but to an amount only to control it and ensure it stays in a prominent position in the public eye, not enough to eliminate it.

en.wikipedia.org emphasis mine

Attrition warfare employs the notion of pyrrhic defeat.