Azure has about 21% market share and revenue of around $15.1bn (sort of, MSFT bundle it with 'Intelligent Services' in their reporting). Someone must be using it. It clearly isn't dead. Secondly, some recruiters are liars who will tell you literally anything to try to get you to apply for jobs they're recruiting for. A recruiter saying MSFT stack is a dead-end just means they don't have many MSFT stack jobs on their…
But the question is if you want to work at the 21% of companies that use Microsoft. Based on my own experience, you probably don't. They tend to be legacy companies in low-growth areas and lower pay.
It's also worth noting that a lot of consulting companies focus on Azure. This is because of perverse incentives, but still worth noting.