It's absolutely relevant, and I would generally agree with you. There is one exception though. If the system is surrounded by a well designed testing framework

It's absolutely relevant, and I would generally agree with you. There is one exception though. If the system is surrounded by a well designed testing framework, it can be overhauled piece by piece as necessary, no system rewrite required. Test code illustrates what the original programmer expected, and enables a system to be extended without necessarily understanding the theory behind it in its entirety. Of course, most legacy systems don't have good testing frameworks in place these days, so it might take a few years to see if this exception actually holds true or if the testing frameworks tend to get scrapped with the system.