BITSAT is more of an exam which demands speed and more of formula based knowledge and approach.
JEE Main follows the same strategy but of a somewhat higher level than BITSAT while JEE Advanced is an IQ based exam.
BITSAT tests IQ to a certain extent with the help of aptitude based questions and English questions. But I must tell all the students of English medium that these are really easy questions.
Also BITS involve a minimum board percentage criteria but this is only a minimum eligibilty thing. It is tough to achieve this percentage if a student hasn’t prepared for board exams well. This makes the admission process a bit tough.