Max, if it is a Robot, I assume all (or mostly) are stiff mechanical elements, you don’t need to have those weighted. Weighting is to deform (more or less) organically.
Robots are closer to the Bone (joints) set up, as bones are stiff mechanical elements (or seen as such).
Here is an example:
There are more options to connect the Joints with the Objects, but I hope the two different versions I have used here illustrate the idea, and no weighting at all.
In that way, there should be no performance problems. A reduced version can be used for the Mixamo “communication” as they care more for the Joint rig than about the details of course.
Let me know if that works, as I have no idea about your robot at all.
Note that even animated elements under a zeroed out Null, can be then placed/constrained to a joint.
My best wishes for your project