I compared the same stages of the throw.
Most of Sidewinder's foot pressure is still on his rear foot when his pump is approaching full extension.
Notice that in his drill move he is pumping more up with his whole body, which is important to understand the differences between you, Feldberg, and him.
I used to misunderstand the following. Sequence + posture.
That action is bringing Sidewinder's shoulder line and posture "up" with it. If he took that same pump more forward (and shoulders and posture with it), it would be even more obvious that the pump is helping bring his momentum forward more like Feldberg.
Why do Sidewinder and Feldberg look different at first?
Relative to Sidewinder, Feldberg is striding more open to target into the "prep step" and then gets fully closed off in the backswing. Sidewinder's move is also a little different because he allows more bent elbow than Feldberg does. That's important to understand what looks a little different in their sequences - once you account for the posture and mechanics I would call them roughly "the same" (and again, was confused by it for a long time myself).
What should you, @vigurr do about this?
Making your whole move like Feldberg would give you an elite throw, and minimally a lot of excellent body learning, so I would never discourage that. Could be that adjusting the pump helps right away, maybe not. I couldn't do it at all until the last two weeks myself. Might make more sense to you & your body later.
Context/long term points
There's a lot I could point out here but you have only been back for 11 days, so I would recommend you only focus on fixing a thing or two at a time for 1-3 weeks at a time.
The reason I chose to point out the pump is because it's always dramatically connected to everything else in the move. Sometimes you need to adjust something else instead. But a bad pump sequence and posture can
definitely spoil the whole move. I might be one of the only other people I've seen around here stick with the pump throughout almost my entire development, so I have usually made most of the mistakes other people make.
IMHO people underestimate Feldberg's move overall. It is deceptively sophisticated while being one of the most "natural" ways to move. I will try to balance the forest with the trees. Marking up your own image there in numeric order, notice that:
1. Feldberg is more aggressive with the disc/arm unit overall. It's always slightly leading his move. It's fine to cradle it back initially in principle, but not when it is causing issues like yours. The disc is more framed or "trapped" within his chest posturally.
2. You might be naturally pigeon-toed, but based on experience I think what's happening is your pump and feet are disconnected, and your feet are scrunching in unnaturally pigeon-toed trying to grab the ground for balance. Feldberg is doing a natural athletic walk into a hop. Because his pump was already framed well within his chest and aggressively forward, he has no restrictions in making the pump build even more momentum in the next step. Your pump is keeping your momentum back, and your leading foot "knows" you are about to be off balance so it is crimping in trying to grab the ground to keep you from falling down.
3. Evidence that you are off balance and that your pump is not actually connected to your shoulders and posture. Can't fake it.
4 and 5.
You are tipping over rather than shifting underneath. FWIW this is one of the most common errors in the x-step whether or not you use the pump. Good pump tends to help it (for me, dramatically). Bad pump makes it necessarily worse because it gets you off balance.
From 4 to 5, you have the problem
Clement is talking about at 5:32- 5:50: your spine is trapped back on your X-stepping rear leg rather than shifting forward with your body onto the front leg. You want that to happen in your One leg drill and standstills, too.
This is all related to the chest "trapping" idea I wrote above.
He describes it as "the pressure coming from the chest" here. You are "letting the pressure/wall fall out the right/rear side like he talks about at 9:00.
I used to have every single one of these problems. They still pop in a bit here and there and I have to drill them back out.
FWIW, everything from 4-5 was WAY easier for me to learn in standstills, and I still work on it in standstills. Unless a player already has elite movement, it is almost certain that they have posture issues that are easier to isolate in their standstills. Learning & relearning the pump in X-step became its own project afterwards. I am often going back to my standstills when I see something drift in my X-step to help figure out what is going on.