This is certainly not the case. Rohan Jain and Aviral Bhatnagar are some of the most followed writers on various social media platforms.
My cousin is a student from this institute. He once told me a story that was told to all the students by one of the professors. It's about Prof. Nanda, Director at IIM Ahmedabad, speaking at Harvard University. He said that the brightest of students go to Harvard Law School and end up at Harvard Business School. He didn’t say anything about the writing skills but mentioned that not all at HBS are bright students. Similarly, not all the students at HBS would have exceptional writing skills.
The same can be assumed about IIM Ahmedabad. According to the professor, IIM Ahmedabad students are capable of-
IIMA graduates are known for their caliber and talent. But here the emphasis is on the diligence that is exercised in academics at IIMA.
Some of the graduates from IIM A and IIM B were once told to write a reflection paper on three important learnings in their life. This was a test for them to be selected for Ph.D. under a professor. None of the students produced any satisfactory answers. All of them wrote in a very descriptive way without being critical and analytical. The professor here is high opinionated but very good in articulation and his writing style.
Not everyone has writing skills like Rohan Jain and Aviral Bhatnagar. A student can definitely improve his/her structuring and writing skills while being a part of the IIMA journey. The journey has always been transformative for the students.