To me the issue I see is this:
First off, this is very common issue with advanced/expert level skiers:
Your “up” is being created by your need to “re-align” yourself before you can begin the new turn.
Let me try to explain:
As you end one turn you outside leg is well behind your mass, and as such your outside ankle is well flexed. Coaches often refer to this as “hanging off the boot”. As you move through the transition you must get that outside foot at least even with the inside foot, otherwise you hip is locked, and your foot is locked, and all kinds of weird stuff happens. Hence the need to re-align before a new turn can begin. The easiest and most natural way to do that is to extend…which you do. This brings your body back to a square neutral position allowing you to begin the new turn.
So the question now is:
“Why is the outside leg so far back in the first place?”
Well this is caused by the mechanics of your turn initiation. When you begin the new turn, you are pivoting both legs…”statically”…this results in the outside foot falling behind, and the inside one going ahead. This is often referred to as a “lead change”. Now this “lead change” is kinda good, because now your outside foot has gone back, or put another way, your weight, relatively speaking, has gone forward. This forward movement of our weight applies tip pressure, which is good of course for starting turns. So this approach does work, and thus used by many strong skiers.
So the question now is:
“So what’s the catch?”
Well the catch is, your mass is being supported by the ski boot, and not your foot, thus you are kinda “stuck”. Your ability to uncouple for/aft balance adjustments with up/down is limited. This causes problems in rutted race courses, moguls, and of course transitions. Sure you are stuck forward, which is better then being stuck back…but if you want to go to the next level the ability to make subtle fore/aft adjustments at all times is critical. Being able to uncouple fore/aft from up/down is one of the core building blocks of great skiing.
“So what should you do?”
Change your turn initiation mechanics. This is easy to show, hard to explain with words, but if you look at the videos of the guy in the yellow pants his turn initiations are brilliant. Notice how his outside foot never gets caught behind? Notice how yours goes back almost as soon as you start the turn? Your first 2 turns show this the clearest.
When “yellow pants” initiates, he is “placing his feet” in such a manner that they will support his mass as it moves into the new turn…he is not relying on the boot cuff or ski tip for balance at all. Hence think of pivoting as more then just turning the legs in the hip socket, but also moving the feet forward on an arc. I know people will jump on this…but think of the move as being similar in action to an up-stem…but with both feet. The video by Tog of the Slalom skier in the white suit shows this well also. The feet turn AND move forward on an arc to always stay in a position to support the COM.
Even if they had no ski tips or stiff boots, they would not fall forward at the start of the turn because their feet are supporting their mass…they are not relying on the ski tip or boot cuff to hold them up…you are (albeit in a very skilled and refined way).
“So if I do this I won’t have a lead change anymore?”
No…you will still have a lead change, just not as great.
“So if I do this, then how do I get the required tip pressure?”
You achieve that by pushing down on the ball of the foot. This is kinda the opposite of what many skiers do…most create tip pressure by pushing into the boot cuff…but creating tip pressure via pushing the ball of the foot down, or “point your toes” etc, is far more effective because it allows the up/down, fore/aft, adjustments to remain independent.
This takes work to fix, but it is worth it. For the record, it is my view that this is the single biggest mistake that cause L3s to fail their L4.