The flex in boots has detriments as well as advantages. The more the skier flexes the boots, the slower and less precise they are for getting the desired fore & aft balance.
My Dodge 130-flex boots are the stiffest I've had, including Nordica 130-flex. The Dodges are the best skiing boots I've had for several reasons including the quickness I can get my balance and the precision to get the balance just where I want it. In bumps, powder, washboard trails, packer furrows, etc., I can weight the tips (descending a bump) or lighten the tips (ascending a lump), get or get centered in deep snow quicker and better than in any other boot I've owned. (Weight the tips going down a drop-off?...Yah, ya betcha. Rule of thumb--if the tips are off the snow you have no control. Pull the feet back when going over a drop off, keep the tips in contact with the snow, and the skier is centered and with the best opportunity for control.)
We know that flex indexes are not comparable between boot manufacturers except some twins from the same ownership--Nordica & Tecnica, Lange & Rossi, maybe Salomon & Atomic. And we know that the actual flex changes with temperature changes (except the Dodge carbon fiber).