Anakin would not kill his son.....hed lose on purpose if Luke refused to give up.. He was all about family in rots...(aside from the force choke on his sweety..lol...)in empire and rotj he had not been anakin in so long he had to see Luke on his deathbed to snap back...but he was fresh annie still in rots he wouldnt have finished Luke off I dont think
The only real fight we see between Vader and Luke is in ESB. Luke had no more training after that, seeing as Yoda died at the same that Luke returned to him.
Vader owned Luke his ass in ESB, easily defeating him. Luke stood no real chance against him then and would not have stood a chance against him in ROTJ if Vader would have wanted him to die, let alone stand a chance against ROTS anakin.
Now about Anakin not killing his son, your right.. Doesn't mean he wouldn't kick his ass though, besides if Anakin would go the future from ROTS he would not even know Luke was his son and still own him.