he gets plenty of practice dealing with players hitting into his backhand with all sorts of spin. feds biggest problem with nadal is he hits into his backhand constantly with heavy topspin and serves into his backhand naturally. if they were the opposite way round handed this would still be the case, as for the fed having a better serve i doubt it, he hits all the spots now. if anything fed might be less of a player left handed as so many players on tour could use their forehands to attack his backhand.
I agree that Fed might be less of a player left-handed, but as for the rest of your points, I disagree. The fact is that lefties make up less than 10% of the population and are just plain awkward and uncomfortable to deal with and this gives them a natural advantage in many sports. Familiarity breeds comfort.