Played as marksman/sneak, and yes, it can seem easy. But I found from chapter 4 on (or was it chapter 3) I was spotted very easily by wilderness creatures even with sneak at 100 and with weak armour ratings became mincemeat quite often. The whole point to me of playing sneak/assasin or sneak/marksman is the ability to creep in and kill with one blow without getting caught and the anxiety of knowing if you are caught you are done for. I think making sneak a little harder to level up in would be more preferable.
If you think its way too easy, could always push the difficulty level up to 100 and see if that helps make the game more enjoyable for you.