I feel like the From Ashes DLC was likely initially meant to be similar to the Catwoman deal with Arkham City.
I would agree with Cannata's opinion of the DLC if the DLC was not so interwoven into the single player campaign that it seems odd to not be there. Especially given that this sequel has less characters to choose from than part 2 and just one new (non DLC) character seems very odd. It seems to me like this character was meant to be a free DLC incentive for those who bought the game new (like Catwoman was), but they decided to charge for it at the last minute.
I usually have no problems with DLC when it is a story that takes place after you finish the game because your initial play-though of the game is not hurt at all. This DLC is more problematic because like Catwoman, you feel like you are not getting the full experience, and worse than Catwoman, it is not free for those who bought the game at release.