Yoda was powerful.. but Anakin had a bigger midichlorean count than Yoda. Or he had in Episode I anyway.
Perhaps Luke is more powerful, but it wasn\'t Luke who turned Vader - it was the love towards Luke inside Vader wich turned him to light-side in the end. Vader saw Luke being tortured and nearly killed, so he finally woke up. The love inside him, the love wich was still left towards his son turned him to the light-side. He killed his God just for the love towards his son. Luke had nothing to do with this process, really. It was Vader\'s battle, and Anakin finally won. I haven\'t readed the books, but I\'m talking about Lucas\'s Star Wars now. The star wars we all know.
And, Anakin turned out to be a \'ghost\' just like Yoda and Obi-Wan. They were all strong, the three strongest in Force in SW universe. Luke was Anakin\'s son, and if Anakin was the chosen one, of course it would effect Luke.
Luke was strong in Force, but not the chosen one, nor as powerful as Anakin. It WAS Anakin who defeated the Emperor, it was ANAKIN who brought the balance to the Force finally. Anakin turned to the light-side himself, Anakin defeated Emperor.