See this can be true or false from different perspectives. If you consider environment and faculty wise then obviously IIT's will have better teachers than the last IIT's. IIT's gives you different opportunities like open placements which you can appear in and pursue your career as something other than your course. Obviously for that the knowledge is required but its manageable if you are interested in it.

Now if you are not interested in the field of interdisciplinary courses then I would say don't do that. Because the work you want to do not so interested will become a pain for you and you will loose your efficiency. So if you think that core branches is the right choice and you can't focus on anything else then just go for it. If you think you can develop the skills like programming while studying something else then go for IIT's it will give you better exposures.

I hope this answer helps. All the very best for your future endeavors!