Its not a question about who would win . Carlsen has the better CAPS and stats so a "prime" Casparov and a "prime" Carlsen based on stats , wich in all fairnes is the only thing we can use to compare quality of chess , would always end up in Carlsens favour . Therefore the queston who is better is obvious . Like comparing a Lada to a Ferrari if you ask me . Carlsen of course the better players as almost every other player of a game or sports are better today then 10 - 20 - 30 years ago . case closed :/ 
“I believe Kasparov would easily win in a match between a prime Kasparov and a prime Carlsen”
No one would easily win a match against a prime Carlsen. Kasparov didn’t win easily against Karpov and Kramnik in any of the six matches he played against them, and Carlsen is a stronger version of Karpov/Kramnik.