It feels somewhat disingenuous to include a turing-complete meta-programming language (i.e macros) in your definition of the C++ type system.

Because vanilla OCaml doesn't have any mechanism for expressing compile-time computations, the same level of transformations aren't possible, but I wouldn't call this a limitation of the type-system, rather the meta-programming capabilities.

Although, you can somewhat approximate it with modules and functors:

     module type M = sig type t val t: t end

     let my_type (type a) (v: a) : (module M) =
       let module M = struct
         type t = a
         let t = v
       end in
       (module M : M)

     module T1 = (val my_type 123)
     type t1 = T1.t
     let val1 : t1 = T1.t
     module T2 = (val my_type val1)
     type t2 = T2.t