I don't know about what's happening in the game but there is a lot of mis-information on the use of the 88mm in combat.
1) In air defense, the 88mm averaged 16,000 rounds fired for every aircraft shoot down. Flak was used primarily to disrupt an air attack not knock down aircraft.
2) I don't have a breakdown for the 88mm batteries, but overall, the static defensive manning broke down as follows: approximately 10% regular air force personal, 50% women, 30% men too young to serve, 20% men either too old or not capable of serving in the front. Basically, not front line troops,
3) Defensively, 88mm was set up in the rear of the main line of resistence with machinguns, light artillery and foward defense positions in front of them. Typically, they deployed in four gun batteries split into 2 gun sections.
4) Offensively, the Germans used the sword and shield approach. The tanks would advance forward, encounter enemy tanks, retreat and draw the enemy tanks back, where the 88mm were sighted in and prepared to take them out. This was the favor tactic across all fronts, and worked virtually all the time. The exception would be if the Germans HAD to advance and didn't have the ability to tactically move backwards - such as Kursk. Or if the Russians, especially, overran the German armor and then rapidly over ran the 88mm line - expensive, but it worked.
The exception, BTW, is the Rumanian oil fields. These defenses were manned full stenght by air force personnel.
As far as city defenses activation, this would require moving the equipment out, providing permanent moving tractors, manning them up, and deploying them. And these units were the "first generation" 88mm which were mounted on high profile carriages - meaning that they were more open to damage by both direct fire and indirect fire than the latter low carriage versions.
Could it be done? Yes, but it should cost both manpower and arm pts to fully activated them. The high AP may already do this, but these units would definitely not be the "best" AT killers, especially later in the war when the Soviets had more indirect fire avaliable.