If turing-completeness were the only criterion to judge programming languages, then we'd be all programming in Brainfuck. Indeed, C++ template system is turing-complete, as well as Scala's. But saying they are more or less equivalent is a complete misunderstanding. The main purpose of type-systems is to prove/disprove correctness-related properties of programs. The better the type system, the less frequently it rejects a valid program or accepts an invalid one.

I could go on and list a number of features that Scala typesystem supports natively which C++ does not (e.g. type bounds, path dependent types, variance control, existentials, abstract types...), but there is no need to do that.

There is one much bigger difference between them: C++ templates are not a first-class citizen of the C++ type system. They are just a (turing complete, but quite limited) macro-language bolted on top. Actually the compiler does not perform any typechecking of generic code. All the typechecking happens after macro expansion when generics are gone, and the typechecker needs to understand only concrete types. This is completely different than in Scala/Haskell/F#/C#/Java/OCaml typesystems, which can reason about generic types and can fully type-check generic code.

All true and all quite irrelevant to the problem at hand. An IDE does not need to know which properties a type system makes it easy or otherwise to prove. It just needs to understand the type system. And a useful C++ IDE absolutely does have to understand the template system and the way it interacts with the type system - maybe a compiler can get away with running them as two separate stages, but an IDE needs to do things with incorrect code as well as correct code.

"And a useful C++ IDE absolutely does have to understand the template system"

I've never seen a C++ IDE that could fully type-check template-heavy library code before its actually used beyond just syntax checking and limited type-checking the non-generic types. This is something that can't be done just because of how C++ templates are specified ("duck-typing"), not due to an implementation detail in the compiler/IDE. This is also the reason why good error-messages from templates are so hard to make - type errors are detected at the concrete level (late), not at the generic level (early). This is going to change when C++ finally gets "concepts" and will be able to reason about generic types (but this would be still a very long way to something like Haskell or Scala has).