The execution plan on each statement will give you more detail on what is happening. Try using some of the provided oracle tools for investigating what exactly is happening in each case.
Try doing a:
SELECT/*+gather_plan_statistics*/ * FROM TABLE(get_data(12345, 'MYTAB'));
then do a:
SELECT/*+gather_plan_statistics*/ * FROM my_view
These will give you the actual execution plan for the statements.
By the way, you will need select on the V_$SQL_PLAN and V_$SQL views to use the gather_plan_statistics as above.