As a compromise extension of the idea of Warding as a combat skill, could Barriers just use the existing combat defensive skills? Has this been discussed? What would potential flaws of this idea be?

You would use your PM and Warding to determine the strength of a barrier, and your Shield skill determines how effectively you use it to defect blows. This would help a bit with the shield skill's slight shallowness in particular, but I could also see the odd Parry or Evasion barrier as special cases.

---

"Warrior Mages don't bother covering up their disasters.
They're proud of them." -Raesh, on history