If the runtime, then I bet almost no one will notice, especially if the appropriate caching is used.
If the programming-time - sure, but it's not like you can avoid parsers altogether. If the parsers are not in the tools, they must be in IDE. Factor out that parsing logic, and make it a library all the tools can use (or a one-shot LSP server if you are in the language that has hard-to-use bindings).
Note even with AST-in-file approach, you _still_ need the library to read and write that AST, it's not like you can have a shared AST schema for multiple languages. So either way, tools like diff will need to have a wide variety of libraries linked in, one for each language they support. And at that point, there is not much difference between AST reader and code parser.