Tbh I do agree to an extent but it's not as black and white as that .Obsidian were given a very successful template to start with and just flesh out while bethesda had to figure out just what approach they were gonna take and ultimately decide what they wanted and what goals for fo3 were .While obsidian were told specifically what sort of game to make and had a template to work from (and see what worked in fo3 and what didn't bethesda had no such luxury) obsidian did well no doubt but thay had it easier in some aspects than bethesda.
Not really and here's why. Fallout 3 uses the same platform as Oblivion does it not? So the engine was already made. Yeah Bethesda saved Obsidian some time by creating skins for people and creatures and animations, but that doesn't justify why Obsidian was given such a short amount of time. The Bulk of creating a game was done from stratch by Obsidian as it was with Fallout 3 by Bethesda. The creating of a story and developing characters and quests and designing locations was all done by Obsidian in far shorter amount of time. Bethesda had three years to do all that and Obsidian less then a year and we got a much better result from Obsidian IMO.
Also I doubt Bethesda told Obsidian what to do and how to do it. I am sure it was more along the lines of "do what you feel is best but run it by us first." Bethesda had the luxury of a fanbase that was willing to by any crap Bethesda turned out (not saying Fallout 3 is crap but the fanbase is very loyal lets just leave it at that).
Obsidian wanted to make Fallout Fallout to please the fans of the Originals and the pressure was on them. They didn't have the luxury of knowing their game would be a hit or not like Bethesda had. Bethesda's fanbase could have eaten Obsidian alive. But thankfully that didn't happen. From what I can see Bethesda's fanbase is starting to turn on Bethesda.
Anyways to sum it up, only a small amount of work was already done for Obsidian by Bethesda. A fraction of what goes into making a game was already done. Obsidian had to make New Vegas from scratch just like Bethesda had to make Fallout 3 from scratch.
It would be like Bethesda and Obsidian making cupcakes and Bethesda had much longer time to make them then Obsidian. In the end Bethesda comes along and puts a few sprinkles on Obsidians cupcakes and takes the creadit for making Obsidian's as well, "Well we did most of the work." When all they did was add a few sprinkles and in the end Obsidian's still tasted better than Bethesda's.