I don’t feel that physical characters have teh advantage at all. Mental characters have a whole slew of options available to them that physical characters do not. The weakest characters are by far the ones that are the most physical for a few reasons:
1) It is much easier to invoke a mental mastery on someone in public than it is to shoot or stab someone.
2) Mental skills have much more use than physical skills.
3) Mental masteries tend to be more powerful than physical ones.
Mental characters have multiple advantages over others. If you want to stack yourself with combat skills, you just made not only an uninteresting character, but one that could be covnerted to a new religion, convinced of anything, or layed out from across the room via skills and masteries.
I understand the need for balance, and ask anyone I’ve always strived for it, but at the same time I think you should look into the real use and roleplay value of mental skills… even the eventual combat value via masteries and put those into the equation. What I see happening here is that a character with mental abilities will end up having as much combat worth as a physical character, plus all those nifty “mess you up” masteries, plus more out-of-combat use.