For me T2 stationary flak is almost never useful. I think it should be stronger considering its stationary compared to mobile flak.
If we look at other stationary defenses like point defenses they we can observe that they are significantly stronger than normal units of the same tier in terms of projectile speed, DPS and range. Just compare 5 tanks to a t1pd, Percivals to a ravanger or a few Wagner to a Cerberus.
Now I feel like T2 stationary flak should be stronger in some ways.
Here are my suggestions:
1. Increase efficacy versus fast moving tier 2 units like torpedo bombers. This would make them viable defenses on navy maps versus torps.
2. Increase their range significantly to make a tier 2 flak a worthwhile investment as preventative measure to cover and entire area against air raids such as drops and zlo bombers. They would still suck versus tier 3 air, but be actually someone useful to get on tier 2.
3. Reduce build time by 25%. This way your engis aren't dead before it's finished 75% of the time.
Kill me now.