Like I said, the inaccuracy and the priority it attracts mean it's only good for gunning people down as they run into doorways or around corners. Inaccuracy means it's only good for volume fire or close fighting (which is bad for someone who is stationary). The priority means that in close and long fighting, you will almost always be prioritized over anyone else; I do mean everyone. The priority is because TTK with the turret is awesome at point blank and you're an incredibly easy shot for a sniper, tank, ha, etc. The only way to play around these issues is to make sure the people you're shooting don't know you're there until they're dead and to fight in the 1-10 meter range with it.
For example, I dropped my turret at the top of the short stairs in the biolab cap/shield gen building (the pair of curvey walkway buildings). I could fire out of the doorway easily, but the only way for someone to have vision of me was to walk into the doorway. I got a ton of kills before people stopped running through willy-nilly and then I still got kills for about 3 minutes while they were figuring out a way to neutralize the building. Wouldn't have worked if that building hadn't already been full of MAX's and other stuff, because they'd just flank with a single person and kill me from behind.
So there are instances where it is very effective, but, in my mind, the only positive the turret has over an AI MAX is that it takes one person to operate while it is laying down fire. My experience is that MAX's essentially require constant repairing if they're fighting. That means at least one engineer and one MAX. The turret doesn't take very much damage at all from small arms and you can replant it every 10 seconds, so you don't need any repairs on it, ever. That advantage is far offset by the disadvantages: 120 arc or so, low base overheat limit, and no mobility. So, in reality, it takes multiple people to maintain that fighting position, as well, to revive the engineer, to prevent them from getting flanked, etc.. Generally speaking, AI MAX gives you both the short TTK of the turret and all of the things the turret doesn't give you.
Because the engineer is already so versatile, I think it's alright for the turret to have a narrow range of applications. There are ways to make it stronger without making the turret OP, but maybe not without making engineers OP. No other class gives you the range of actions you get from the engineer.
Slot 2: Pistols (okay not here)
Maybe they'll patch an actual flare launcher and implement it as a secondary, like our fireworks launchers.