"The syntax is this way to make lexing it easier" is not a good argument for syntax. Ever. Lex it into tokens, parse it using semantic analysis, and be done. Plenty of compilers have been doing this for a long while now, and plenty of work has been done to make this a non-problem. Choosing syntax because it's slightly-easier to implement but slightly-harder to use is not a recipe for adoption.
The problems with the lexer hack are user-facing problems, not compiler-writer-facing problems. They include typename, order of declarations being significant, weird function pointer syntax, and the most vexing parse.
I'm not advocating for the lexer hack. There are non-hack-y alternatives, hiding this pain from users. The options of "the lexer hack" or "identifiers first" is a false dichotomy. There are many ways to lex and then semantically analyze programs, and I do not understand why you are arguing as if that is not true.
What’s regular for computers is also more regular for humans. You’re absolutely right that taken to an extreme, doing things for computers isn’t great, but neither is making a super complex grammar
Regular has a technical meaning here, that is, Chomsky’s grammar hierarchy. It’s where the “regular” in “regular expression” comes from. That said, I’m using it in an imprecise way here to mean “simpler to process.” (This is because regular languages are simpler to process than say, context-sensitive languages.)
Location of the type is about grammar complexity. Rust’s grammar plays into its type inference capabilities, and the pattern syntax. There’s an underlying uniformity with syntax elsewhere.
The example of typename shows that it’s a problem that can’t be overcome by the compiler, so it’s trading off one bad syntax for another, not trading off bad syntax for difficulty to implement.
