I assume the command processing was simply not a predictably small enough of a workload to fit into the time budget for an ISR. Besides, that is irrelevant for his point, he already gave an example of a "big" ISR, it doesn't have to be even bigger.
> not a predictably small enough workload
Which means ISRs can grow too big. And that’s the reason keeping ISRs as small as possible should be your goal.
I mean, I (and most people on this thread...) agree with you, I believe it is almost always "nicer" to be consistent and have minimal ISRs. But her/his point (as I interpret it, at least) was that in some situations a somewhat larger ISR may make sense.
That's not a good argument. That an extreme is bad doesn't make the opposite extreme good. I could easily have a house that is too large, but I wouldn't want to live in a box.