Yes but this in no way qualifies him to be the leader of the Wardens --- if one is looking to reform the Wardens in any way that requires a level of honor and integrity that you find out Blackwall does not really possess.. He did after all murder women and children to get the families money-- and then he waited until the very last of the soldiers under his command as Chevalier Thom Rainier was about to be executed before admitting to his crimes and probably only then because the guy would have seen him acting on behalf of the Inquisition and outed him.. .. I would not put him in charge of one of the Inquisitors nuggalope's forget about an entire organization in major need of reform.
Clarel and all ranking Wardens are dead. A Senior Warden is left as acting Commanding Officier which if you know Warden hierarchy you'd know that it's a respected rank, but not that high. And certainly not privvy to all the secrets the entail the Order.
And along comes Thom Rainer who was recruited by a Warden-Constable has a vial of Archdemon blood, a Joining Chalice, Grey Warden journals/treaties/deep road maps, Grey Warden songs and banners.
The highest ranked guy which is only two ranks above Warden-Ensign (which is basically what the HoF and Alistair were at Ostagar) is gone. And you're a recruit with all these things and experience....
Yeah.