Michael Spivak wrote about this concentration of complexity in definitions, in another context of mathematical abstraction - in differential geometry / abstract calculus. Here is a quotation on the topic, from the preface to _Calculus on Manifolds_:
> The reader probably suspects that the modern Stokes' Theorem is at least as difficult as the classical theorems derived from it [classical Stoke's Theorem, Green's theorem, the Divergence Theorem]. On the contrary, it is a very simple consequence of yet another version of Stokes' Theorem; this very abstract version is the final and main result of Chapter 4. It is entirely reasonable to suppose the the difficulties so far avoided must be hidden here. Yet the proof of this theorem is, in the mathematician's sense, an utter triviality -- a straightforward computation. On the other hand, even the statement of this triviality cannot be understood without a hoarde of difficult definitions from Chapter 4. There are good reasons why the theorems should be all easy and the definitions hard. As the evolution of Stoke's theorem revealed, a single simple principle can masquerade as several difficult results; the proofs of may theorems involve stripping away the disguise. The definitions, on the other hand, serve a twofold purpose: they are rigorous replacements for vague notions, and machinery for elegant proofs.
> Concentrating the depth of a subject in the definitions is undeniably economical, but it is bound to produce some difficulties for the student.
To what extent can these observations be carried over to category theory?