What happens if you switch the stick to Flight mode?
This is an xbox manual, but there should be a switch that causes the throttle to be seen as an axis, and disables the analog stick on the top of the flight stick. That's how prior iterations of Hori HOTAS function:
https://www.manualsearcher.com/hori/ace-combat-7-hotas/manual?p=3
(Also, you could cosplay as that guy from Gotham with all the guns.)
Edit: from an Amazon review:
"The latter one is quite problematic. According to the official HORI instruction manual you are supposed to choose throttle switch Setting 1 when you want to use the throttle for acceleration and deceleration of your jet fighter, but in my (particular?) case that only did work in Setting 2."
(I think this might be a PS3/PS4 switch on yours. If it only works on PS3 then yeah, you're screwed)

From what I gather, that means Setting 1 is most likely what you're looking for (the opposite of what works for AC7, as the Xbox manual seems to indicate). You'll need to remap the throttle, of course (and probably all the other movement controls).
Let me know if I've solved it.