Where did someone get the idea that the grey wardens are all highly skilled?
Duncan was conscripting anyone that was good with a sword because it was a blight, and they lacked numbers. These grey wardens do not have the same luxury of having the power to conscript anyone (Since i highly doubt that any nation would let them do that in big numbers)
We only saw two grey warden armies before (Ostagar and Soldier's Keep) Ostagar was a failure and their number reduced to two grey wardens (Alistair and the HoF)
One is a companion and the other is the player character their power is greatly superior compared to most people at the end of the game. But even then, they are exceptions (Otherwise, the HoF would not be so special)
Then there is soldier's keep, where it was an highly defendable base, and the base was in good state, even then, things got desperate enough so that summoning demons would seem a good idea.
Here we have a base in bad state, an army overwhelmed (If you play your cards right, it's orlais + the inquisition attacking them) with most mages trying to bind demons (and some grey warden warriors sacrificed for that purpose, so they weren't at full strength)
If they had won that battle, they would have became the biggest mary sues of the entire series, unless they are inhumanly capable, they have very little chances of winning the battle against the inquisition (Who at that point in the game would have a capable army, depending on what missions one has played before, the inquisition might have orlais + mages/templars + soldiers given by nobles + templars who defected to the inquisition at the start of the game and peasants with high morale and good training as it's army)