not being able to do RS with RCE is so dumb, the chart says that RS can be used with any power that requires range and another argument is that the charectors need to concentrate to use RCE but why? They are experts after all, Why do they need to concentrate?

Well, think of it as this:

A character has a range of 10 and Running Shot at a speed of 8. The enemy is exactly 10 squars away. You can either use RCE or perform RS. Perform RS, and you move up 4, putting the enemy away at 6 squares. You no longer need to be an excellent marksman or markswoman to hit the enemy. No reason what so ever to get the boost for being an excelent marks man/woman.