Which IIM don't have higher academic weightage in throughout selection process?

Every IIM has their own criteria. Some are heavily academics oriented and some are less academically oriented. In older IIMs, IIMA can be good for those who have diversities, in term of academics. Last year, they had increased the weightage of cat score in final composite score as compared to the previous year.
IIMB gives heavy weightage to academics.
IIMC is a savior for those who have bad academics. They give full score for those who have above 80 percentage in 10th and 12th. And best thing is that they don't consider graduation score.
IIML looks for 12th and graduation scores. It gives equal weightage to work ex also. So, if you have 80+ in 12th, 75+ in grad with descent work ex then you can expect a call from this institute at 99.6 percentile.
IIMI is again putting heavy weightage to academics.
So, in nutshell, IIMC, IIML and rest new iims give less weightage to academics as compared to IIMA, B, I and S. If you get 99.8+ in cat then you can expect calls from 2-3 older iims.
P.S- I have provided these informations based on my personal experience. Please don't take it for granted because every year some iims change their criteria. And data which are provided are approximation.

See there is no IIM which don't have any weightage throughout the selection process. Each IIM OIL has fair % of weightage for academic records.

It varies from college to college generally each college gives 25-30 % of overall weightage to 10th, 12th and graduation marks in the aggregate score which is used to make up a list for calling students for interview round. This weightage reduces further around 10-15% in the final aggregate list which is to select students for admission.

There are even some college like IIM Kozhikode which gives 0% weightage in final aggregate list as there is more weightage to interview, WSAT and GD.

Apart from IIM Indore which gives a lot more weightage to 10th, 12th and graduation marks even more than CAT marks and IIM Bangalore who prefers to call students with a lot of work experience or the one who have done extremely well in 10th and 12th like scoring above 95% in both exams, all other IIMs gives an avg weightage to academic records.

Aim for a very high percentile in order to overcome the loss in marks due to not so good academic records. All the best for your preparations and exams!!

Although the criterion are refined every year, based on the past trends. IIM Kashipur gives comparatively lesser weightage to academics as compared to IIMs of the 11th Commission.