Asset optimisation

Dear fellow developers.
Curious if any of you have thoughts regarding this.

I have written some code for Maya and Houdini that writes out a json file containing a list of assets with position, scale, rotation. And in Unity I then run over the json and instantiate prefabs in edit mode. I make sure to turn on the static flag for each as well.

And though I now have let's say 300 trees in my scene, they are instances from only 3 prefabs.
I'm hoping that this is of course better than having built a layout in Maya, then export it all as one big geometry.
But is there an even better way?
Is there any back draws doing it the way I currently do it?.
If anyone has any ideas on how to better handle thousands of assets such as trees houses and rocks,
I'm super keen to know more.