It does improve productivity, just like a good IDE. But engineers didn't get replaced by IDEs and they haven't yet been replaced by AI.
By the time its good enough to replace actual engineers, any job done in front of a computer will be at risk. I'm hoping that will happen at the same time as AI embodiment in robots, then every job will be automated, not just computer based ones.
Your assertion was not that "an engineer has never been replaced by AI". It is that no engineer has been laid off because of AI.
You agree AI improves engineer productivity. So last remaining question is, does greater productivity mean that fewer people are required to satisfy a given demand?
The answer is yes of course. So at this point, supporting the assertion requires handwaving about shortages and induced demand and demand for engineers to develop and support AI and so on. Which are all reasonable, but it should become pretty apparent that you can't be confident in an assertion like that. I would say it's pretty likely that AI has resulted in engineers being laid off in specific instances if not the net numbers.
By the time its good enough to replace actual engineers, any job done in front of a computer will be at risk. I'm hoping that will happen at the same time as AI embodiment in robots, then every job will be automated, not just computer based ones.