So I imported a model into Blender that already has vertex groups and a skeleton. I then imported a metarig and made it the exact same shape as the imported skeleton. I applied the armature modifier and deleted the custom skeleton and then I made another armature modifier and set the object to the Metarig. The mesh deforms fine. So then I generated a rigify for the model and it worked out fine. However, I went to the DEF bones layer and I saw that the arm and leg bones were subdivided. So I then set armature deform of empty groups to the bones and I renamed the original vertex groups to the arm and legs vertex groups. I then cut the weight paint in half for the subdivided bones manually like so:[![enter image description here]]
But when I pose the arm, the mesh deforms incorrectly at the armpit:
What should I do to fix the mesh deform problem? Auto weights is not an option because this model has too many accessories like a crowbar and many pouches. Thanks for your time.