Muratori was even wasting his time arguing against programmer time _in general_ is less valuable than machine time? And doesn't understand that LLVM is an extremely specialized piece of software, from which general software engineering practices should not be extracted?
Inheritance hierarchies aren't exclusively what he meant though. Interfaces and the whole 'prefer composition over inheritance' style of programming has the same fundamental problem Muratori is getting at: both inherently constrain a program's structure for, what he argues (and I agree with), has no benefit to the program's performance or the programmer's time. In fact, he argues that the constraints imposed by the use of inheritance/interfaces only slow programmers down.
His raw device driver example, in pt2 of their conversation, illustrates the advantage of procedural code over inheritance/interfaces. His API requires users to provide a function pointer that will be called whenever an event is raised. This API user is expected to switch over the enum values that they care to implement. This design is better than an interface that requires its members to implement read(), and write() functions because it is both more performant (no vtable overhead + compilers can make more aggressive optimizations) and more flexible (a new event can be added to the enum without requiring all the old code to be updated if they don't need to handle the new event type).
I don’t think people agree on this (I don’t at least). I like the story falsely attributed to Steve Jobs about how saving a user 1 second will save hundreds of years or whatever. From that perspective, programmer cycles are way less important than CPU cycles because every CPU cycle you save has a multiplicative effect depending on how many users you serve. And how true is that today when you have thousands of large business apps depending on one cloud service provider. The compounding effects of saving CPU cycles in every level of the stack has never been higher than it is today.
But Martin was originally saying that a program with DI will not be as fast as a program without DI ... i.e., interfaces!
When was the last time you were writing a program and thought that putting a class behind an interface would slow things down too much?