The upgrade from a Mini 1 to a Mini 2 is very worthwhile. A lot of people have done so as the 2 offers so much more over the 1. I won’t drift off topic here as the subject has been covered to death in the last 18 months. Pull up a chair and have a read of the mega thread: DJI (Mavic) Mini 2
Getting back to the original question, what makes you think the storage case is causing your props to turn too fast? 
Have you studied a flight log in detail?
Is it always the same rotor that’s spinning faster that the others?
Have you swapped the props around to see if it makes a difference? Or replaced all four for a new set?
I probably have more questions but will stop typing now 