> Today, the criticism about complexity seems naive, because many later languages have become much more complex than Ada

I don’t think you really understand what you’re saying here. I have worked on an ada compiler for the best part of a decade. It’s one of the most complex languages there is, up there with C++ and C#, and probably rust

Mind you, that suggests that the sentence is at least half-true even if "much more complex" is a big overstatement, since Rust, "modern" C++ and the later evolutions of C# are all relatively recent. (What would have compared to Ada in complexity back in the day? Common Lisp, Algol 68?)

As a matter of general interest, what features or elements of Ada make it particularly hard to compile, or compile well? (And are there parts which look like they might be difficult to manage but aren't?)

what do you mean under Ada's complexity? E.g. C++ is really complex because of a lot of features which badly interoperate between themselves. Is this true for the Ada lang/compiler? Or do you mean the whole complexity of ideas included in Ada - like proof of Poincaré conjecture complex for unprepared person.

I imagine Swift is also a very difficult language to compile.