How to make a non-convex meshed object affected by physics(non-kinematic)

I'm new to Unity so there's probably a simple solution that I don't know about, but I have been searching endlessly for a solution to this but I can't find anything.

When I have an object with both Rigidbody and a Mesh Collider(with custom mesh) it doesn't let me use that mesh without enabling "is kinematic" in a rigid body, but I want this object, with its complex mesh to still be affected by other physics objects. This object is already low poly, and I only plan on rendering one in the scene. That's the best I can describe it in words, here is a 20-second clip showing what I mean

I know at the bottom it says that "a non-convex mesh with a non-kinematic rigid body is no longer supported since Unity 5" but besides the improved performance, why does Unity not allow this anymore, and how do I get around this? Thank you very much to anyone who can help me out this has been driving me insane for about a week now lol.

P.S I know I could get around it by manually sculpting a mesh collider in Unity, but I really don't want to have to do that. I'd really like to be able to use the mesh of the object.