IISc isn’t underrated, instead, it is not overhyped. As Indians, we tend to put our financial security above everything else. IISc is known primarily for its research and there is a common perception in our country that a career in research is not very financially stable. Also, while the media heavily praises and highlights the grand packages of other institutions, IISc is not given much limelight for its contribution to the field of research. In fact, the research of IITs, NITs, BITs, NSUT, etc. isn’t given any publicity as well. We focus more on salaries and job titles, and give less importance to research.
For a student who knows his field well and closely follows the developments in Science and Technology, IISc is a very respectable and admirable institution. Getting into IISc is not a cup of tea, it requires a lot of hard work and dedication.
Thus, IISc is as good an institution as IITs, NSIT, BITS, NITs, etc. You should definitely join it if you want a career in research.