IMO, the Tempo is the overall speed of the swing going back and forth…and Rhythm is how good the transition is and how in sync the swing is.
I have yet to see tempo that is too fast, but tempo that is too slow is awful.
I believe good rhythm and tempo can mask bad mechanics.
I do not think perfect mechanics can mask bad rhythm and tempo.
I also think better rhythm and tempo can be taught…as I have done so for many of my students.
I think many people over do slow tempo and absolutely destroy their rhythm.
As I said, I don’t think people have tempo that is too fast. They confuse tempo that is too fast and bad rhythm.
You can have a fast tempo and great rhythm (Nick Price). Very few people have ultra slow tempos and have anything but horrible rhythm…as I said above.
The object is to find a tempo that you are comfortable with that isn’t too slow, expel all but one or possibly two swing thoughts from your mind…and good rhythm will likely follow.