I don’t know about “vertical”, but the pitch-up theory is the NTSB’s own, not the sole assumption of the person you’re responding to.

It's not an assumption.

Here's what a tail-heavy 747 does: https://www.youtube.com/watch?v=7sUWC2jfjqI

you will notice a rapid lack of upwards ('vertical') movement in that video.

You’ll notice it’s taking off, not at cruise speed, and still makes a thousand or more feet into the air.

Unfortunately I can't find altitude graphs or anything for national airlines 102, so can't really back up my argument with facts, but I'm gonna take a guess and say it wasn't flying like a rocket vertically upwards for 1000 feet. My guess is that it would have stalled very quickly after it nosed up too far and started dropping.

You make a good point about TWA 800 being at cruise speed compared to the cargo flight, and let's assume you're right and it does manage to nose up and keep going for some time: in that case you'd see something go upwards after an explosion, not streak towards it - though eyewitness accounts in times like that have been known to be flakey, so i give up here.

> in that case you'd see something go upwards after an explosion, not streak towards it...

Unless there's a subsequent explosion of the now-burning half a plane.

There's a good set of animations on https://imgur.com/a/zin7CRo that illustrate the theory of what happened.