At the same time, you get a mushy tree as input, instead of a properly typed AST "object" with accessible "function name", "method parameters" everything that you can just refer to.

It will be the third arguments' 2nd arg with s-exprs, following your arbitrary pattern you figured you want to use. So it's very arguable which is easier to use, sure for some "party tricks" lisps will win, for anything more useful my vote would go with rust/Scala macros for sure. So again, you win nothing by homoiconicity, the by-the-compiler implemented parse function is more complex in rust, which is 100% abstracted away.