No it's not. Breaking a world record in any track and field event is much more difficult. Only one other person in history has set the record. 99mph fastballs are hit every day in the majors. Even by some mediocre players.
To further illustrate my point, I could actually make contact with a 99mph fastball by pure chance. However, I can't "by chance" run a sub 10 second 100m.
Ok, I should have said "hit a fastball/curve/slider/sinker/changeup" consistently on a regular basis, and not just once in your life, like a world record is. Can they get up and do it every day?
I think the fact that the most successfull hitter (based on BA) of all time still failed 63.3% of the time illustrates how truly difficult hitting a pitched baseball is. There is no other sport where that rate of success would equal skill.