A nerf to vertical mobility against Mobula to bring it a little bit closer to the other ships would be kinda alright, but what really keeps the ship in the engagements are top speed and its horizontal accerleration. Fish trying to circle a Mobula? Oh what is that, its horizontal acceleration matches the Goldfish'? Why, don't mind if I Stamina Kerosene and turn right around to shoot it into its side, annhilating its 400 armor, keeping the hull engineer away from the engines, snipe the engines with no effort from that range and finish of the kill on that stationary Fish!
Flying up and down is nice and all, but it doesn't keep guns aimed at what is actually close. You may lose gun arcs against the Mobula, but the Mobula also loses gun arcs against you. Just predict the predictable hydrogen and then proceed to outmanouver it on the horizontal plane or if it didn't pay attention and is in front of its ally, proceed to casually fly past it, focus firing its ally while it is still trying to turn around.
Being able to move all 5 of its guns back into arc on the horizontal plane against even the fastest ships in the game was the real problem. The same went for the old Metamidion that had enough horizontal and turning acceleration to Gatling and Mortar literally everything, regardless of their speed and health.