Without being able to look through code its sort of hard to say one way or the other how efficient of a job they do. Further complicating matter is that some devs code the engine at one level and then the engine is used to build the game through an editor interface on a high level. There are seriously way too many factors to just guess at this.
I can tell you I know I wouldn't want to build an engine at an Assembly level, but it would be damn efficient if done right. I'm pretty sure a lot of engine work is actually done on this Assembly Language level as it tends to need that kind of efficiency.








