If a method has no async operations inside it there's no benefit in making it async. You should only have async methods where you have an async operation (I/O, DB, etc.).
If your application has a lot of these I/O methods and they spread throughout your code base, that's not a bad thing. But don't just add the async keywords on synchronous methods.
In your specific case ExecuteQueryAsync benefits by being async as it allows using await cmd.ExecuteReaderAsync(). GetTableColumns and GetDataFromReader seem to be CPU intensive methods and they don't fit they async-await paradigm.
