For this achievement, all you need is to have 21 stars TOTAL. You do not need to 3-star the maps that came with with 2016 Batman v Superman Batmobile (The Wayne Tech Track Pack). I just got 21 stars, and the achievement popped right away. I actually found that the handling was very good on this Batmobile, so this should not be too difficult. With all of the additional maps now (1989, Tumbler, and 1960's) you no longer have to 3-star every race, and can also say goodbye to having to do 3-lap races!
At this point, you can do whatever tracks you are best at to get this achievement. I only did the single lap races, and I had no issues. Below are the maps you can use, and I have put my results in parentheses.
- Penguin Dockyard (2 Stars)
-Batcave Set (3 Stars)
-Ashes (3 Stars)
-Cataclysm (3 Stars)
-Cobblepot's Causeway (3 Stars)
-Joker Parade (2 Stars)
-Midnight Fury TT ((Time Trial) 3 Stars)
-Cauldron Speedway TT ((Time Trial) 2 Stars)
-Crushonator (Riddler Course)
-Condamned (Riddler Course)
-Mental Blocked (Riddler Course)
-Batmobile Proving Ground
Don't forget you can also do some Hybrid Maps as well:
-Seek and Destroy
I did not even touch the following:
-Penguin Dockyard: 3-Lap Race
-Batcave Set: 3-Lap Race
-Joker Parade: 3-Lap Race
-Ashes: 3-Lap Race
-Cataclysm: 3-Lap Race
-Cobblepot's Causeway: 3-Lap Race
-City Heat TT
-Batmobile Proving Ground: 3-Lap Race
With all of the above, I believe there is the opportunity to earn up to 69 stars, making this achievement much easier than the others.
Hope this helped! Happy Gaming.