We only got trials for the three based on Zeon mobile weapons from Gundam.

No, really. Emerald is the Neue Ziel, Diamond is the Qubeley, and Ruby is the Baund Doc with the arms of a Hygogg. And while it only appears in a cut scene in 7 and a solo fight with the G Warrior in 14, Sapphire is the Doggorla. The Ultimate Weapon is the only one in 7 that doesn't look like a Zeon suit.

Incidentally, the G Warrior is a pile of Gundam references. The general beastly design calls to mind the Barbatos, the hair cables like the Nadleeh, the butt skirt boosters and the G Savior weapon pods resemble the Dendrobium, and the triangle shield was used by the Nu Gundam. (G-Saviour was also the name of a live-action Gundam movie, but we don't talk about that.)