I think the flakhq is stupid though. 0 pop, free with teching bofors that gets repaired by sturmpios (which run circles around everyone else) and has a pretty good range and the ability to penetrate allied mediums. You don't have to put it front and center, you can just cover isgs with it and they're basically invincible if you go t1. That's what I do when I play okw and I don't feel like using pumas (love that unit).
The FlakHQ is a nice mechanic I think. It has a high level of risk reward and players have to think strategically about where to put it. You could argue either which way on it's damage and pen rates but the mechanic itself I feel is a good one. At the heart of every good RTS is calculated strategy and risk reward mechanics.
If you place it too far forward and use it for defence you risk losing 120 fuel and your ability to field any tanks in the mid to early late game, so it isn't always the best idea (depending on the map and how the front line moves in the match).
Repairing it with Stormpios is not as risk free and easy as you make it sound. If the HQ is being mortared and you are trying to fix it, you risk losing a 300MP squad to one stray mortar. Stormpios are super valuable and a heavy cost to replace, not to mention difficult to vet past 2 or 3, so losing them is big.