I'm on the fence with this theory, according to the OP a good hairline seems to deem a good galea but make someone bald and the galea would look much larger and 'expanded' brad Pitt for example, perfect hairline, would look like a huge galea if he was clean bald, like many pictures on this thread.
However there is definitely some merit to the theory that skull/jaw/chin development is somehow related to scalp tension and hence some forms of hairloss. It's just not so clear cut as the OP seems to promote imo.