Im not sure I really agree with this, unless it's "it's like having an engineer mic a cab for you, but without them knowing anything about you or what you're trying to achieve". An engineer mic'ing your cab in real life is probably going to know what the music is that you're trying to record, what gear you are using, what suits the aesthetic you're going for. And they'll probably take your own personal preference on board.
Using a pre-made IR is more like sneaking in the studio at night on someone else's session and using their mic position for yourself. It might be perfect, it might be totally inappropriate.
Even moreso for any IR's that have EQ slapped over them. An actual audio engineer is going to make those decisions based on the circumstances and what they hear, and what they are being hired to do. Slapping it on an IR without knowing where it's going to be used is nothing like an engineer doing it with purpose. Micing up a cab and processing it is very much a reactive process based on a lot of variables. Anyone can plug a mic in and place it in front of a cabinet