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The weird thing is they repeatedly talk about hypersonic flight and the objects coming to a sudden stop and turning on a dime., It was shocking to hear and see the Secy of Defense saying that the only two possibilities being extra terrestrial or another nation having developed more advanced technology. Is the latter a possibility? Or how about a third possibility- since we have found creatures with alternate biologies at the deepest depths of the oceans, so how about some kind of creature that exists high up in the atmosphere?
I mean, sure, in the land of hypothesis anything is possible. But the thing is that the motion is just part of the speculation; to establish the actual motion of an object in 3D space you need at least 3 variables measured over time. The pilots only had 2 measurements (the two axis of the screen to locate the object or maybe the 2D coordinates of the point on the surface of Earth just behind the object as seen from the pilot perspective). You need to know another variable (it could be the distance to the object or it could be the altitude of the object over the surface of Earth) to correctly study the trajectory.
In the Gimbal video, for example, the object appears to move extremely fast. This is also commented by some "authorities". The object also seems to slow down quickly, so quickly as to appear to have superhuman resistance to accelleration. But this is just appearence. The object could be moving slowly but beeing much closer than expected. The object could be even very far away and still move slowly if our pilot is moving fast (this is not because the pilot might have move faster than human experience allows but rather the fact that even at moderate speed when there is enought parallax things look as if they where moving strangely). In fact, in the Metabunk discussion (that I recommend as a read again) they show that the object could have even been completely still in the air and even then the Gimbal video would make it look like it was moving at non-conventional speeds.
I know that this is one of the impressive cases, where there is some reliable data, and there are even some "authorities" that express the UFO view-point. But it has been shown that 1) the data is insufficient to actually establish the "weirdness of the movements", 2) that there are other more conventional phenomena that show exactly the same behaviour (so, believing is something else is just a leap of faith), 3) that authority does not matter in science (even if the head of the Pentagon stated that he saw an UFO, an investigation would be needed and the evidence should be as public as that statement is) and 4) even if we believe in authority, these people are not scientists, nor they are supporting their view on the expertise of any research team, their authority is not even in the field they are making statements on.
Finally, suppose we are really in front of undisputable evidence of non-conventional aircraft movements. I totally agree with you that assuming it must be aliens is just unimaginative and shows the lack of creativity of some persons when it comes to formulate hypothesis. They could be visitors from another time, not from another place. It could be a secret military operation of another country or one performed by the same country but a different agency or even performed by the same agency but so secret that only a small team in that agency has been allowed to that level of secrecy. Maybe is a new creature we haven't heard of that lives in the atmosphere as you said. It might be a vehicle created by a submarine civilization that is always hiding from us, or some intelligent species living in the depths of Earth's crust that have only their gate to the surface in a remote part of the world and then they fly around. Why aliens? Is it really aliens more probable than the time-travelers? "Oh they are in the sky so they must come from space! a region of reality that I associate with the sky because I'm a superficial monkey (I live in the surface)". The fact that we all think in aliens when confronted to these stories probes the lanscape of our pop culture and folklore, stimulated by cinema, TV, radio and press. UFOlogist tend to think of themselves as "out-of-the-box" thinkers and see scientists as cold, uncreative and arrogant, when the thing is that they are the strongest adherents of mainstream views and socially constructed views as to how an alien must behave and what an UFO really has to be, while scientists are always searching ways to blow our minds, to destroy preconceived notions about everything around us and would be the first ones to encourage the analysis of non-conventional data results.
These UFOs are just planes sadly. But even if they were not, humanity has shown again how less we are willing to actually know and explore different possibilites. If we were visited by something trully strange these people would actually do the worst analysis of the situation, not the skeptic-minded scientists at all.