altitude being an important word there, air density playing a big role in these stability modes
Quite true,
However, there were other problems with these very early B707's that might not be appreciated by younger folks.
The yaw damper (parallel type) had to be switched off for takeoff and landing, and an approach in a very gusty crosswind could become a rockin'-an-rollin' affair, and it was
not a pleasant experience.
The series type yaw damper fitted to later aircraft solved this problem to a large degree.