And right now, the Alliance isn't just taking hits from Blackbird without fighting back; they've made an equivalent retaliation.
The Blade Tiger spent a whole day bombarding Blackbird City from orbit until they ran out of ammunition, and only then did they cease.
Blackbird isn't like the missile silos the Alliance targets; they have no countermeasures against orbital bombardment. They neither possess anti-orbital firepower capable of exchanging blows with the Blade Tiger, nor the ability to deploy an elite land force to board the starship.
So, they just had to endure the bombing.
It's a pity that it's the Blade Tiger, not the Quintet; otherwise, the damage to Blackbird City wouldn't be limited to the outer city. The entire core city would be blasted to ruins, and energy shields would be useless.
But it's okay if they can't blast it to ruins at once; they can always resupply ammunition and continue bombing a few days later.