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.
