I've played both tennis and baseball pretty extensively growing up. I was a damn good pitcher myself. Went to Renz baseball academy, went UGA baseball academy, and really perfected the art of mechanics used to pitch, I should have kept playing, but I hated my highschool coach and teammates full of sweetheartry. I've been hit in the face 3 times, one was a curveball, and it hurts like SOB.
I had started to get into tennis a few years earlier. Then I started really getting competitive with it, joining tournaments, going to camps, and playing on the highschool team.
The biggest decision I had to make was tennis or baseball in highschool as they were in the same season. I had played freshman year baseball and just hated practice and only playing every other game to pitch, so I decided to stick with tennis instead, it was a lot more fun to play, better excersize, and not as strict.
I really should have stuck with baseball because I had no idea how stiff the competition was in Atlanta. It really shocked me on how good some of these kids were, and I considered myself pretty good. It was then I realized just how hard tennis was. I was playing top 50 ranked players in the state who were damn good, but they didn't even compare to the top 50 in the south, and they didnt even compare to the top 50 in the nation, and most of them don't even compare with the top 50 in the world.
It's amazing how good you have to be to make it in tennis, and actually live off your winnings.
There is no coaching during the match, no teammates to help you, and its running back and forth up and down for hours while being mentally tough to make the right shots and win the match.
So while baseball has the hurt aspect of getting hit by pitches, or getting hit with the ball in general, which Fing sucks! Tennis is a much more physical and mentally draining game than baseball is. Being a pitcher has its mental notes and high pressures don't get me wrong. But tennis on the mental level is a whole different ball game.
So you can say what ever you want. But I'll back it up by saying tennis is much harder physically and mentally than baseball as well as more rewarding as you get all the credit being the only teammember. Winning 4 grand slams like serena is about to do, or winning 17 grandslams or more in mens like federrer has done, pretty much takes way more effort and skills than it does in baseball.
I love both sports respectively. But playing both competively opened my eyes to how physical and mentally draining the sport really is.