90% of people buy boots that are too stiff
TLDR: buy some medium flex boots unless you race.
I just bought a new pair of boots and have to make this PSA.
I worked in ski shops and on the hill from age 17 to 27, selling, as a tech, and shooting video for the advanced ski school. I'm proficient at skiing all conditions on and off piste. I enjoy all kinds of skiing (park, race, etc.) but focus on big mountain powder and cliff drops. I'm big and ski aggressively.
For years I skied in race boots because they were the best boots (fitting and performance wise) you could buy.
The last pair I bought a few years ago was at a shop that was going out of business and I got a great deal on a pair the fit me great. I brought them home, googled the boot and was surprised they were an "intermediate" boot. They were exactly the same as the "expert" boot but with a softer flex. I figured I'd give them a shot and I loved them. I can ski all day and my feet never hurt and they work great in most conditions.
In race training and lessons a drill you do is to ski with your boots completely unbuckled. The people who complain that they can't do it are the ones who's weight is too far back. It teaches you to ski balanced and then you don't need your boots cranked down.
When you ski you want your weight forward with your shins pressing against the boot tongue. If you can't bend your boot forward enough your weight won't be in the right place. About the only time I can press stiff boots far enough forward is on a race course or hard snow at high speed. I mainly try to ski powder, a stiff boot will not flex enough to stay balanced. Even on hard snow a medium flex boot will bottom out it's flex range and you can still transfer power to the front of the ski when the cuff hits the lower shell.
I just bought another pair of boots. I went to a few stores and tried on everything in my size. Almost all of the boots were 120 or more flex. I bet I'm more proficient than 90% of the skiers who buy boots there, but 90% of the boots were too stiff for me. I found a pair that fit me great, then found the softer flexing version (everything else the same) online for less than 1/2 the cost of the "expert" boot.
I know park / freestyle riders have known this for years, but it seem like all mountain skiers are being sold boots that are way too stiff and getting overcharged for them.