For starters, soft boots do not help prevent shin bang, nor does any brand of ski boot. The only things that prevent against shin bang are having the right size boot, right volume for your foot, a footbed, the right fit of the tongue against your leg, and a flex that is appropriate for your weight and power.
With that said, you never want a stiffer boot simply "because". If your current flex is appropriate, going stiffer will only put you in the back seat and lead to bad balance and poor skiing. However, if you can appropriately flex the next stiffer boot in the lineup then it will give you some benefits. It will be more supportive on bigger landings and also be more efficient in many ways of skiing- edge to edge quickness, buttering control, etc.
Most all of our athletes are on 120+ flex boots. Keefer, Gus, Andreas, Elias are on the Overload 120, Jossi, Byron, Riddle are on Redster 120/130, Benchetler and Sage are on the Waymaker Carbon 130. But these are also strong powerful skiers used to stiffer boots because softer boots will simply fold underneath them.
But always remember that the right flex is what is right for you. Softer boots do not fix shin bang and stiffer boots do not necessarily lead to shin bang- only the proper fit and flex for you will prevent against shin bang. So try on the next stiffer tongue or model to see if it is something you can appropriately flex.