> The lack of .h files alone is a huge grievance for me

That's an interesting point... Besides C and its derivatives, and OCaml, do other languages have separate definition files? It seems like newer languages, even statically typed, normally don't.

I suspect the reason is that you have to duplicate all definitions, which seems like rote work. It also feels less necessary with IDE tooling: IDEs I know have a view for all definitions in a file.

They don't, but, at least in object-oriented languages, much of overall experience is easy enough to replicate with formal interfaces and coding standards.

I thought the nice thing about Modula-2 was that you could browse through interface files to understand some code and then go into implementations.

It's true, but there are so many ways to skin that cat. Smalltalk, for example, gives an even more fluid way to browse at a high level and then drill in, and it doesn't (necessarily) have source code files in the first place.