The difference is zameen asmaan ka faraq.
I have October 2019 Alto. I recently got 75W oil in it. And its a alot better now. 1 to 2nd gear is Slightly felt, but the jerk isn't there. Just a change of gear as you feel in any old automatic transmission car.
Simply speaking 90W oil is around rs.450 a liter while 75W costs around rs.3000 a liter.