We've seen that also. You interview someone online, help file the paperwork to get into the country and work visum, and then someone else, a technically much weaker guy, shows up on the first day. We had that twice in the last two years
This may be a reasonable gamble, as many companies do probably not expect such a rochade, and do not have detective measures in place. And if that doesn't work, you still have 3 months time to find another job in an environment that favored job seekers at this time.
[1] https://expatrist.com/losing-a-job-in-germany-with-eu-blue-c...