I haven’t read the entire posts but I’ll just add some of my thoughts on my experience with Unity to Blender.
Unity doesn’t like bendy-bones (actually no software other than Blender likes bendy-bones). So I’ve found that it is better to use 2 rigs when exporting to Unity.
1 rig that does all the deformations and 1 rig that does all the controls.
Then after it is animated – you export all the baked animations on the deformation rig.
This means that Unity has 1 rig with zero constraints – which means less chance of things going wrong.
(I won’t say zero chance because stuff always goes wrong haha)
Good luck – and don’t give up the fight. Software is dumb, people are smart. You’ll win eventually.
