I am not saying ballet is easy, you could come home from ballet with bleeding toes and strained muscles but from jazz you could come home aching a little bit. I am a ballet and a jazz dancer and I love them both but i think we all agree that ballet takes a lot more effort to stand enpointe for an hour then jump around.
To be a ballet dancer, you need to be disciplined and extremely dedicated. Also, ballerinas need to be very strong, especially when going on pointe. They have to do high jumps, do complicated footwork, and balance on the tips of their toes, and they have to make it look graceful and effortless.
Yes, ballet requires more physical effort than jazz, because ballet requires more strength. Ballet moves require precision, and very specific, controlled movements. It takes a lot of stomach muscles to do the controlled movements in ballet. Jazz is a brighter, easier form of dance. Ballet dancers make it look good, but it is not as hard as ballet is.
Jazz, although it looks more free-form, requires a high level of skill and physical dexterity. The types of movements and muscular strength probably vary between these two types of dance, but I can't
think of any type of dance discipline or form that could be classified as less strenuous than another. All disciplines would seem to require their unique moves, and an overall condition of physical fitness.