"Cavalry" are traditionally fast-moving & hard-hitting formations, often used to screen friendly forces or flank enemy ones. Many armies had armored (tank) formations inherit the traditions of their famous cavalry units -- but generally not until the tanks were fast enough to leave infantry behind.
In this case, I think we can posit the "cavalry" formations as being fast light armor units -- especially hovercraft. As the existing "armor" units in the LCT are specifically listed as Heavy & Assault units (and thus, no doubt, slow), it makes sense for the LCT to also include lighter armored units, but also for these light units to be faster. The Scorpion, despite being a light tank, is no faster than a Manticore, and so would make a poor choice for inclusion in a "cavalry" unit (unless the Heavy & Assault units were overtaken with things like the Behemoth, which makes even a Scorpion seem "fast"). The Vedette & Galleon (among non-hover designs) would be good choices for a "cavalry" unit.