With a Yacc-like parser, it is indeed hard to define what the AST should be, but because AST generation is most of the time rather straightforward, you could automate it, by simply specifying some string at the end of a rule and have a generic mechanism for dealing with the option, plus and star-operators. For an example of such a grammar for C have a look at: https://www.iwriteiam.nl/c_gr.txt and for a parser which can interpret this, have a look at: https://www.iwriteiam.nl/MM.html

Only a few people are working on developing production compilers, while much more people will have to work on simple parsers at some point during their working life. If performance is not crucial, I believe it is better to use a parsing system that is easy to use and does supports EBNF.