While that was true for quite some time, it has dramatically improved to it's current state such that it is only noticeable during peak 'tatkal' booking time.
The UI is horrible, but the UX is quite functional. And given the millions of people with various degrees of tech-savviness who use it, it's probably a good thing they haven't done a major revamp in years.
That still shouldn't prevent them from iteratively, slowly fixing the UI such that people have to only get used to small bits at a time.
It is one of the most unintuitive design I have seen. It only works because we're trained to it's quirkiness.
I also feel the UX is horrible because it will often log you out and demand that you log in again if you have performed a set number of actions repeatedly.
The UI/UX is still horrible though.