Sacred Haven of Debauchery

Since you're arguing from a realism perspective, two corvettes won't completely halt production.

Debatable. Small, fast projectiles can hit other small corvettes in space over long distances. That is, they have high accuracy and obviously considerable firepower. You can produce something on a planet, but only under enemy fire, so the efficiency will be... and there will be a large number of constant human casualties.
In reality, this translates to the probability of destroying a production facility for an entire sector, which, with intensive bombardment even by two corvettes, is not that small.

And if a large fleet is doing this, it still can't establish control over the planet, it can only wait for everyone to die of starvation. And the existing army will be shooting deserters and panicking people who want to surrender on the spot. So, in principle, everything is correct; the fleet can hang around in the air as much as it wants, but without ground control, the benefit of this will be limited.

And in the game, the planet wasn't captured; military points were simply awarded. This is more than logical, considering that such a planet cannot build a spaceport and consumes resources for maintenance, giving nothing in return.

Yes, I thought of something else - what kind of fleet would be needed to completely make it impossible to grow turnips even on such a small planet as Earth? In general, if we go further in realism, it is likely that such a policy will not work, and they will not be able to take anyone by attrition.

I agree about the food crisis. But here, it's like in Heroes - you sit in a castle, waiting for your fate without mines. If they can't take you now, sooner or later that will change anyway...