What are the limitations of DrawMeshInstanced() with dynamics gameobjects ?

I'm trying to make a scene where there are a lot of moving objects.
They have a rigidbody component and share all the same mesh to render.
I noticed the framerate is limited by the rendering of the meshes. one batch per mesh.
So I tried to reduce batches by using Graphics.DrawMeshInstanced(), but the result are not so great.
The issue is I have to feed this function with an array of matrix4x4. One matrix per mesh instance. Iterating each update through all the objects to get transform.LocalToWorldMatrix is costly.

Am I doing it wrong ?
Is there a better way to instance the same mesh for a lot of dynamic objects ?