The programming language doesn't really have anything to do with difficulty. It's hard to code in assembly these days because nearly no one does it.... if you are unfamiliar with a language of course it seems harder. Guess what everyone was using to code games in the 70's? That's right, assembly.... so it didn't seem hard at all to the programmers of the day.
Now if he has been picked off the street and expected to learn assembly and make a game in 5 weeks your point would have been valid, but since he already knew it, the point you are trying to make falls apart like loose sand.
No Warshaw was picked up by the management at Atari, coded a game in five weeks for the Christmas market and the company bankrupted it self due to mass manufacturing of the said game and due to returns. I can remember I returned mine for frogger. Games cost $59 back then and you got one for Christmas or your birthday.
Even if Atari made millions of Yars Revenge (and the sequel which is pretty good) carts, the very game Warshaw had to sell to management to get the game made, the console would have died a death anyway. I can remember how many pacman carts they made too. Plus the Sears variant which had it's own carts.
Assembler? You have to squeeze and juggle code in to make the game work. Not an easy task even for the early 80s, as Raiders took 6 months to develop, and we are talking 1980s here and not 2016. So my comment is pretty accurate, compared to languages available today like C++.
Probably why Warshaw was chosen and not David Crane. Crane would have told Atari to piss off.