You can't possibly get autocompletion on x. and y. for that first select if you didn't write that from clause yet (or at least the autocompletion you'd get would not be tailored to those tables).
If you add the table name you could, and that's what "x." here is.
So yes, you can autocomplete
SELECT employee.Na<TAB>
to "employee.Name", but it requires you to type the table name "employee." first.
But with the from-first style you can autocomplete even bare column names - you know you have "name" (possibly even "employee.name" and "supervisor.name") and "employeeID".
Except that the table name isn't necessarily going to be that x. If you are matching employees with their managers then you have two employees tables in that expression so you have to work with aliases. At which point autocompletion breaks down.
