The last of those videos is the most clear:
What's nice is that the video starts and ends on the ground - and is completely un-cut.
I grabbed this photo from near the beginning, when the camera is still on the ground:
...and has a nice, clear, high altitude shot (this one is at t=1h51m14s):
Of course we must eliminate all complaints about the lens - so we can take that first shot and draw some straight lines on it:
That clearly shows that whatever distortion there might or might not be - it preserves straight lines as straight lines - which is all we care about.
Then we can draw a straight line across the shot of the horizon at altitude:
...and clearly it's showing a significant curve...as expected in RET for a flight up at 100,000 feet.
The video is high quality - the levels of realism are FAR beyond even the best computer graphics available. The guy who did this has a YouTube channel. And it's pretty clear from watching it that this is not any kind of official NASA thing - it's just a guy who likes fritzing around with old weather balloons and cheap cameras:
https://www.youtube.com/channel/UCQ9Q9nFLsMZihAGf0k-uUBwAbout 4 minutes into this video...
...you can see the balloon he used - clearly happening in the same neighborhood as the video that I took the still images from.
Seems like it's REALLY a stretch to call this "part of the conspiracy"...it's unreasonable to say that the video could have been faked...and for 100% sure there is no significant camera lens distortion involved. He even tells us that he swapped out the GoPro's standard "fish-eye" lens for a more appropriate lens. So we don't expect significant distortion - and we don't find any in the imagery.
This is about as clear a demonstration as I could imagine. Calling this "faked" is an act of desperation here!