Agree with @Provin915 regarding engineer overall. The rate of fire increase itself is great incentive, and I personally love to take advantage when I'm playing all star for example, but some other suggestions I want to throw out there regarding ammo regen if it were to be nerfed - perhaps instead of "infinite" ammo, reduce the ammo replenish rate, so its like players would have "double" ammo capacity before overheat occurs or before having to reload. Or one step further, don't replenish ammo, but improve the reload times to twice as fast. Those are some "in-between" solutions aside from removing the ammo regen attribute entirely.
Something I read about often, as far as engineer actually supporting instead of playing selfishly, I think it's easier when the engineer knows the spots to plant the turret and other players can then join and take advantage. It's rather inconvenient to follow a random player around to support them with a turret, it's not like a sunflower heal beam, and other players can be unpredictable where they are moving or trying to go. Not to mention, there is a 15 second penalty when the heavy helper gets destroyed - this makes engineer think twice about where to plant it.
Nonetheless, there are quite a few great spots I can think of in Turf Takeover such as behind the statue/fountain on the first and third objective of Peachy District. Other spots are harder to describe but they are definitely out there on the TT maps. I've had instances playing engineer where certain players would follow/join me where I place the turret throughout Turning Point and other maps so I can say there certainly are engineers out there playing in the supportive role with teammates taking advantage! Finally, in terms of map design, the developers do seem to appropriately limit the number of very strategic positions to place the turret, it would be OP if every objective of every map had "perfect spots" to support the team.
