$stored_type should return an array or WP_Error, see this link.
$posted_type should return the value which was selected in the form.
With this value you create an a term object/array, see here.
Now you should have 2 values to compare.
I think you should look into defining $_POST[‘acf’] differently.
AFAIK (but I can be wrong), the fields are only defined by key and not by name.
So I would change
$_POST['acf']['field_picktype']
to
$_POST['acf']['field_key']
like I did in my example.
If you don’t know how to find them go to Custom Fields > Field Groups > Your group > Screen options > Check Field keys.
