That is completely correct. In lisp, the fact that syntax is so flexible enables the addition of a lot of functionality on top of the base language. Types and related functionality (checks, enforcement, conversion, etc.) is one of those things; but if everything is executed on top of pairs, there is a performance penalty that you may avoid if you provide more efficient data structures from the onset with a not-so-minimal implementation (such as clojure providing vectors, where you dont search a list in linear time). My “just” above meant that if you can do it slowly in the upper abstraction level, providing it in the lower one is basically an optimization.

In any case in second thought what I said is not completely true, as there are things you may need to do in compile time and the minimal implementation does not provide macros.