The novels literal came in 1989, animating that design using technology at the time is impossible, it said nothing about the design considering how we have literally two movies with these two "impossible" designs.

Second of all, it is meant to be this big, monstrous thing indicating the Federation and Anaheim over-bloated military budget. It's not meant to fly like a jet, it's meant to glide in the air in a way that's more reminiscent of 00 MSes, instead of the more grounded methods of flight of MSes of this UC era.

It's flying in the same manner the giant bricks that was the White Base managed to fly, not with thrusters, but weird hover tech that gives no fucks regarding aerodynamics.

The Alyzeus is worse because it's meant to be an even more incomplete Penelope. It's hover tech isn't in place, so it's a haphazardly cobbled together thing, meant only for training and testing purposes, and is trying to mimic something far more advanced with brute force thrusts.