So what are these Ph.D. engineers doing, then? Sitting at home with their degrees waiting for a big enough offer? I think not. They are employed somewhere, which means that actually they are not counterproof of a shortage.
Raising salary always comes up as the "answer" to the talent shortage, but it's a highly localized answer. Sure a company can fill all their openings by raising their salaries--they'll do it by recruiting currently-employed engineers from another company.
That doesn't "fill a hole" industry-wide. It just moves it to another company. If there are more holes than qualified engineers, there's a shortage.
To make the case that talent shortages are caused by low salaries, you'd need to show me a lot of people who are qualifed but currently willfully unemployed, waiting for the right offer. I'm not aware of many engineers who fit that description.