I tried Mesh 2 Motion. It seems like a pretty solid system overall. However, it seems Mesh2Motion simply was not designed for an A-pose with the arms this close to the hips. It seems to use spheres around the bones of a fixed size to detect nearby topology, with no way to configure the sphere size or repaint bad weights. Unless I've missed something?
Feel free to upload yours. I tinkered with it by hand using Rigify, but then I got lost in the sauce making a secondary UV-map so I could rebake the textures into something that would be a little faster and easier to make new textures for using photographs. Before I knew it, it was midnight and I was seriously considering making a new base mesh.
Let this be a reminder to all indie game devs: Feature Creep is always a hazard, even in modelling!
Here’s my Characters PSX file I used for my game jam entry: Metro Macarena
https://drive.google.com/file/d/1blPK-jhDBn_-TFsN9eqUEXLES3EVyp4W/view?usp=sharing