I can not comment on JIPMER UG, but replacing AIIMS UG with NEET UG is not the best decision in my opinion.
I have given both the exams in my time, and NEET has a huge luck factor involved in it. Moreover, the AIIMS entrance was way tougher, especially the logical part, so it had a better differentiating ability.
Scoring in NEET is much easier, which is not good in my opinion. No entrance exam should allow a score of 700/720. Now a huge number of aspirants are scoring high because of which, limited vacancies have a very high number of claimants.
So according to me, this was a bad change for serious aspirants.
One of my friends is preparing for medical exams and he opposes the idea of scrapping AIIMS UG and JIPMER UG exams. People that this gives them an advantage like: -
However merging the exams have led to the real advantages the students had before which are: -
AIIMS was on the level of engineering entrance exams comparatively NEET is much easier therefore there are lots of students with the same marks fighting for a single spot.