Automated testing and debugging are not the same
99% of the time, I debug using tests. You write the expected output and then fill in the implementation. If you don't get what you expect, something is wrong with your code and it is easy to run it in the debugger to figure out what is wrong.
At the end of that, you end up with a test and some code that works.
Other people call this TDD.
Yes. They made their own purpose-built debugger. It's a tool that makes it easier to see what the program is doing. Your debugger is no more or less valid than their debugger. It's a tool, and the best tool is the one that enables the programmer to accomplish their goal. And that's what they did.