Or do what should have been done since day 1-make it a side cost upgrade.
OKW is getting enough freebies in tech and utility as it is.
No need for them to be that special snowflake all the time.
No, that's like, a terrible idea, because the whole build animation revolves around the 2 crewmen setting up the flak cannon. The animations are particularly detailed and awesome. Since such things are part of the overall game-design and create atmosphere and a positive visual aspect, why remove them.
The change you propse would require new animations where the flak cannon is not set-up. The current animations as it is would become useless. This is not desireable at all, as it is one of the most detailed special animations in the game; and it is such beautiful details that make the game what it is. Without them, no matter how suppossedly great something elusive as a perception of balance may be, the game cannot be such a compelling experience.