Is it true that IIIT Delhi is very strict, completely academic-oriented, and only people with very high interest in a CSE should only join there?

Academics is the top most priority of IIIT Delhi. Everything else takes a backseat. This may be because it is branded as a research institute. 

If you wish to pursue research in CSE or complete your MS/Ph.D. from a foreign university, choose IIIT Delhi. Academically, IIITD is comparable to IIT Bombay, IIIT Hyderabad, etc. But don’t choose IIIT Delhi if you are planning for an MBA later on. In this case, you might end up dropping out due to a loss of interest in this course.

As for placements, more than 95% of B.Tech CSE students are placed each year. However, very few non-tech companies visit the campus. As ECE receives very few core companies, students from both branches compete against each other for tech jobs.

Based on your own priorities and goals, decide whether or not to choose IIITD for your CSE course.