If we know we are weaker in anti-spy, we should upgrade our anti-spy to the maximum if possible. A shieldless cruiser should not be underestimated if a fleet of destroyers decides to try to dismantle it.
The real problem can be caused by the ground defense of the enemy planet if he chooses, and he puts everything back on him. In the meantime, he will build as many tank factories as he can handle. By blocking the process, it is worthwhile to specifically destroy the stronger ones with spies, because based on the ground simulation, we will have less loss compared to rocket forts, for example. Even type 2 space defense cannons don’t have to be dealt with by spies because strong ships quickly crash.