This looks really good. Nice improvement.
Two small pieces of advice. Make the artwork for you:
In this case you could use different shaped platforms, to allow players to quickly see what turret is what without zooming in. Even if just simple shapes; in fact using simple shapes as a foundation is a great idea.
Second, use references:
Even professional artist uses references. Lots of artist use simple shapes to make complex art. https://www.deviantart.com/tugodoomer/art/env-obj-52-573913173 Looking at their work should inspire some of your own ideas.
I Like the depth of the platforms and your roundness looks visually correct. Good work.