Being able to do a high quality, consistent job assembling engine after engine is not a huge feat, it just takes a lot of attention to detail. Being able to spec out and effectively execute a particular engine build is on a whole different level and the latter is what I'd be more inclined to call a "craftsman"
The former doesn't need to care (but they likely do since anyone with that job probably does automotive stuff as a hobby) about things like how camshaft specs, rod length, piston velocity, intake design and about a million other variables interact with each other to affect performance of the whole system. The latter needs to be intimately familiar with them while also being able to do the job of the former.
To put it in terms more people on HN will understand, the guy assembling the engine is like the user of some backed software stack. Sure they might write some scripts that interact with parts of the stack but they're nowhere near as well versed in how does what it does and why it does things the way it does when compared to the engineer who designed and built the stack.
Vocational training is still somewhat widespread in Germany (for jobs like mechanics, hairdressers, even sys admins, some more rote programming jobs, …) also as an alternative to going to university.
Now, I’m not sure whether typical assembly line workers have that kind of education (probably not? but I’m not sure), so having someone with this kind of education assemble your engine for you might be a step up, but I also think there is a mismatch going on here between what the English words seem to imply and what the German word means.
from 2014: http://www.bloomberg.com/news/articles/2014-04-06/humans-rep...
(1) Robots are not great at improving on their own work in the same way that humans naturally are.
(2) When he was a boy, Mr. Toyoda recalled that there were always a few men around the factory who were capable of extremely creative and ingenious solutions to difficult problems of logistics or fabrication, and he feels that this skill is being lost.
Anyway, this has been a major consideration for the current management at Toyota for some time.