D was designed by Walter Bright (who played a large role in inflicting C++ on the world) and Andrei Alexandrescu so you could say that...

That's a rather unfair characterization. He wrote the Datalight/Zortech C++ compiler. He was never--that I recall--a big flag-waver for C++.

Anyway, I was joking — Walter did one of the first (if not the first?) "Proper" C++ compilers, so the idea of not learning from C++ is rather ironic.

While we might disagree on a lot of semantical things on this, I'd argue that D very much learned from those mistakes. There's a strong argument for D's templates to be "templates done right" (which C++'s most certainly aren't).

So I encourage you to read more into this topic. To me, this question seems just about as uninformed as someone complaining about a LISP tutorial on macros, asking "did no one learn from the mistake that is the C preprocessor?".

If/where there are other models better suited for metaprogramming would be another (interesting) discussion (full of tradeoffs, I'm sure), but the notion of proper (hygienic?) templates not being adequate anywhere can certainly not be inferred from C++'s implementation alone.