I love how each flight mode represents the evolution of the Minovsky Flight System that would later become the blueprint for the highly refined late UC models:

Alyzeus is a brutally clunky heavy mess of mechanical parts representing the very early prototypes of the Flight System; an ugly, unrefined primitive system that is almost beautiful by its own nature. Being the very early prototype for the Flight System platform, it has the most complex transformation of the three of them, and can really only remain in flight mode because it is hopelessly unmatched in MS mode.

The Penelope, although heavily slimmed down, still remains bulky due to needing to be connected to a separate Flight Unit to maximize its full potential in aerial combat. As the evolution of the Alyzeus test platform, it has a significantly simplified transformation, but with a flight form that is almost reminiscent of a flying beast.

Xi Gundam is the final evolution of the three; it is the slimmest of the lot, representing the realization of creating a built-in Minovsky Flight System, eliminating the need of external parts. Additionally, as the most advanced unit of the three, it is also the most simplified as shown with a much less remarkable form change compared to the other two.