The difference between wood racquets and old string technology versus new racquets and modern string technology is HUGE. Old racquets and strings cannot even come remotely close to producing the shots that are created today. Its an entirely different sport.
Athleticism (speed, agility) would only go so far with younger MacEnroe versus older MacEnroe.
The closest comparison I can come up with is if I play a pusher who was much faster and more agile than me and very consistent. Well guess what.... I destroy these types of players. The pusher has nothing to hurt me with because the shots simply don't have enough on them to bother me. When I am not bothered, then I am in control of the point because I am the one running him all over the place. It doesn't matter how consistent he is when the point leads to him being off the court in 5 shots or less and the next shot is an easy winner.
The same would happen with young MacEnroe(wood racquet) vs old MacEnroe(modern tech). The spin and pace of old MacEnroe would bother young MacEnroe using his wood racquet. You simply do not have the control to overcome the faster shots and heavier spin from the modern day racquets with the wood racquet.
This doesn't necessarily mean you miss the shot right away, but your not going to be able to do what you want with the ball. And that in turn leads you to losing control of the point and being put on the defensive. Point lost.
Young MacEnroe(wood racquet) with his speed and agility still loses, because control of the point is lost.
Someone might point out that serves with wood racquets can be almost as fast as modern day racquets. Poncho Gonzalez comes to mind, but with that we are talking about strictly velocity of a serve. When you add topspin to the mix, that is where everything changes. None of the old time big servers were able to create big kick serves with wood racquets. When you watch the old videos they were lucky to have any kick at all. And this is why groundstrokes are not comparable either. The topspin and pace just isn't there.