Would anyone care to share why perl can do tr/"/'/ faster than s/"/'/?

Because s/// has to be able to handle all RE syntax and specialness while tr/// just considers its input to (mostly) be a simple character class. Much easier to deal with and, thus, much faster.

bbfu
Seasons don't fear The Reaper.
Nor do the wind, the sun, and the rain.
We can be like they are.