No, you should not judge any MBA degree on the basis of the difficulty level of exam. It's a way of conducting exam by different colleges. CAT exam is conducted by one of the old IIM and especially for admission in IIM. Although being one of the most popular exams it's score is accepted by most of the colleges for giving admission.

Now if question paper is difficult then it will be difficult for everyone and you will be getting good percentile even in low marks because everyone will have a hard time and if it is easy then you will need to get very high marks for good percentile because everyone will be scoring very high. So what I mean to say these are competitive exams used to evaluate students among each other so that the best students are selected. So you don't need to judge on the basis of difficulty level.

Also what I think is IIMs make CAT exam a little more difficult because the number of students appearing in the exam is way higher than any other MBA exam held in India. So with an increase in difficulty level, it is easier to sort out the gems whereas IBSAT exam is only conducted at 9 ICFAI business school.

Obviously, IIMs or some of the private colleges in which you get admission through CAT exam are way better in every aspect then IBS colleges. So you can compare your future with the quality of college in which you are going to pursue your MBA degree rather than the quality of exam.

On an individual basis, if I don't compare IBS with IIMs or other top private colleges that some of the IBS colleges like IBS Hyderabad, Gurgaon are decent colleges.

All the best!!