Pickleball is different from tennis with respect to court dimension, net size, ball type, paddles used and many more.
The ball has a lesser bounce in pickleball. Also, there is a volley zone in pickleball, unlike tennis.
The main difference between pickleball and tennis is of serve. The rule of pickleball is that service is made underhand, while in tennis, service is always made forehand.
The height of the tennis ball is supposed to vary somewhere between 53% and 57% of the drop height while bouncing.
If we talk about which sports have more cardio, Tennis would be our answer.
The shots in pickleball should be more precise and perfectly-timed as the court is much shorter.
Tennis balls, unlike pickleball, give higher bounce and executing low shots in tennis is lesser tricky than the pickleball game.