For a start, I'm a major Turret user in Horde. Always have been. But here's the catch, I hate it when teammates use a turret I use tons of money on and just waste everything and then in Deployment thing rebuild it, So they're easily getting higher turret level. I have reached Level 4 Of turrets without EVER Doing this. But most people I see in Horde do this.
Furthermore, I find it annoying how much you have to get to level them up. By Level 4 I had 92807 Spent on them. Now I need more than half of that to Level 5.