I fail to see how an array makes debugging say a routing directive easier. The issue is generally incorrect names or values which will not be aided by a backtrace or a var_dump - you know the value in either scenario. You will still have to dive into the parser and understand what it's looking for to resolve your problem or delve into XDebug.

In the situations when knowing the value of something does not help, I do not see why annotations wouldn't be superior.