For the longest time, we had a situation where air defense guns were pretty hard to use effectively and were really struggling to justify taking up a spot in a player's CORE.
We wanted to address that, so in addition to patching them and increasing their power, we also improved on the scenario design of the DLCs to further promote the use of AD weapons.
We're pretty happy with where AD units are right now. They are finally showing up in the single player campaign in decent numbers, (both 88s and a few self propelled versions in DLC 1943, 44, and 45). They are also very useful in multiplayer scenarios, if a side losses the air superiority battle, they pretty typically fall back on purchasing AD units as the battle continues.
Besides, the dual purpose 88 has a lot of history and notoriety behind it, and we really wanted players to enjoy it and see how effective it was for themselves. Effective as it is, and with its bonus dual purpose mode, they don't show up in a player's CORE very often, which is the perfect place for them to be. Strong and useful, but limited in purpose. This makes sure that our players are encouraged and rewarded to use them, but keeps it from being purchased excessively.
Most COREs seem to contain 1 or 2 88s:
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Going into DLC 43 and onwards, a lot more players are using the self propelled AD units too (definitely a result of scenario design, the Red Air Force gets pretty serious in those later years), which is perfect.
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Harmful to gameplay? Nah.

Harmful to gameplay would be players never using AD units at all, or using them too much.
In the end though, players can always tweak the values, such as RoF, for themselves if they want to adjust the game as they see fit. One of the wonderful aspects of Panzer Corps is its ability to be modded and tweaked.
