This is one of the exceptions of the rule "old is gold". It is because at times this coaching was the best of all in preparation for IITJEE in India but things changed in a very short span of time and now all that glory is lost. It can be easily gauged from the results of its students in last 4 years.
I remember when I was preparing IITJEE there during 2008-2010, the Bansal classes was at its peak with best faculty in India in all the subjects.It had the best curriculum of all others.
The performance curve was upwards inclined because of the exceptionally talented faculty members like Ninja sir, M.S.Chauhan sir, ANA sir, and many others to name. It was the combined effort of these teachers and the students that made Bansal classes a brand.It started losing its influence and glory because of the failure of its administrators who could not keep-in with those teachers who one by moved to other coaching institutes putting Bansal onto the decline each year.since then it has not been able to regain its position till now.Other players have moved in and have gained influence.