I haven’t used MetaHumans yet, just fascinated by the attempt to work on performance and make this game ready. Since you have figured out the performance influence of bones, I suppose a lot of things that are now bone animated could be faked with transitions between normal / displacement maps (wrinkles, folds in hands, bone rotation on the lower arms.) Now this is all just a wild idea and I’m not familiar with the MetaHumans setup but I know this is one way to do it alternatively. It reduces bone and vert count at the cost of shader complexity and / or memory usage.
I mean #(&%(@ this bone count is ridiculous, what is the face like?