[klibertp]

"Essential" here means something that cannot, in any way, be further removed from consideration. In this view, things that simplify the understanding and make the program more practical are not essential - they are add-ons on top of the most primitive computational model(s). You can drastically simplify the reading of the lambda calculus by giving it direct support for integers, for example - however, you now polluted the model with an additional element that you need to describe and always keep in mind. Using Church encoding lets you get integers without introducing any new elements to the model, keeping the model simpler - but yes, the implementations of programs within that model will get much more complex to read.

[brazzy]

Yes, I get that. I just don't think that interpretation is a good fit for the concept, since that was formulated from the POV of practical usability and cognitive load.

Though... now that I think about it, maybe it does fit - it's all about the question "practical usability for what?"

I suppose that if what you actually want to do is model and reason about theoretical computability, then most things that make languages convenient to implement things in actually are accidental complexity!