I think this is great advice, but saying that PL design is done already isn't really true. Its not as hard to make a new kind of PL as you might think, but it is of course hard to make it useful.
Just combining the right features and forgoing the wrong ones into a language alone is an art, to say that its only innovation is a bit like claiming paintings are innovations because we have all the colors :)
I’d explore the various Lex/Yacc based tools after. Hand writing your own recursive descent parser is a lot of work. EBNF sugar and some regular expressions is much less work. Of course parsing is just the first step and you still need to create other representations like ASTs.
Just combining the right features and forgoing the wrong ones into a language alone is an art, to say that its only innovation is a bit like claiming paintings are innovations because we have all the colors :)